NIOSH HEALTH HAZARD EVALUATION REPORT:

HETA #99-0321-2873 U.S. Department of the Interior Grand Canyon National Park Grand Canyon, Arizona

April 2002

DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health PREFACE

The Hazard Evaluations and Technical Assistance Branch (HETAB) of the National Institute for Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and Human Services, following a written request from any employer or authorized representative of employees, to determine whether any substance normally found in the place of employment has potentially toxic effects in such concentrations as used or found.

HETAB also provides, upon request, technical and consultative assistance to Federal, State, and local agencies; labor; industry; and other groups or individuals to control occupational health hazards and to prevent related trauma and disease. Mention of company names or products does not constitute endorsement by NIOSH.

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Ann Krake, Joel McCullough, and Brad King of HETAB, Division of Surveillance, Hazard Evaluations and Field Studies (DSHEFS). Field assistance was provided by Loren Tapp. Desktop publishing was performed by David Butler. Review and preparation for printing were performed by Penny Arthur.

The authors would like to thank Sergeant G. Douglas Fritts, United States Air Force, for his loan of the core body temperature monitors and Ms. Lindy McCollum-Brounley, formerly of HTI Technologies, Palmetto, Florida, for her support and guidance in the use of the CorTemp™ monitoring system, as well as HTI’s generous equipment loans. Dr. Thomas E. Bernard, University of South Florida, College of Public Health, provided essential guidance on the report’s content for which the authors are very grateful. Finally, the authors would especially like to thank the study participants, including park volunteers, park rangers, and park management.

Copies of this report have been sent to employee and management representatives at Grand Canyon National Park and the OSHA Regional Office. This report is not copyrighted and may be freely reproduced. Single copies of this report will be available for three years from the date of this report. To expedite your request, include a self-addressed mailing label along with your written request to: NIOSH Publications Office 4676 Columbia Parkway Cincinnati, Ohio 45226 800-356-4674

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825 Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be obtained from the NIOSH Publications Office at the Cincinnati address.

For the purpose of informing affected employees, copies of this report shall be posted by the employer in a prominent place accessible to the employees for a period of 30 calendar days.

ii Highlights of the NIOSH Health Hazard Evaluation A

A Evaluation of Heat Stress in Grand Canyon Park Rangers

In Sept. 1999, and June/July 2000, NIOSH representatives conducted health hazard evaluations at Grand Canyon National Park. We looked into management and employee concerns about park rangers’ exposures to high temperatures while patrolling and hiking into and out of the canyon.

What NIOSH Did What Park Managers Can Do

A A # We measured the outdoor temperatures in the # Decrease the work load of those hiking out by canyon and on the rim. We also measured how using mules or helicopter transportation. much work (work load) the rangers did. A A # Create a heat stress program that will: # We weighed the rangers before and after their < assess employees for medical fitness before they hikes to test for dehydration (not enough water in begin hard work and especially during the hot their bodies). We took blood to look for signs of season; hyponatremia (not enough sodium in the blood). < allow employees to get used to the heat A (acclimate) before they work in it full time; # We measured the heart rates and body temperatures < train employees to know the dangers of and of the rangers while they hiked in and out of the protect themselves from working in extreme heat; canyon and patrolled the inner canyon and the < encourage employees to report any heat stress South Rim. A symptoms and signs; # We talked to the rangers about their jobs and asked < keep systematic records of employee reports of them to tell us their health concerns. heat stress illnesses; A < teach employees to monitor their own and others’ heat stress and strain signs. What NIOSH Found A # Install outdoor showers and/or use ice vests to A prevent employee heat stress and strain. A # Inner-canyon and south rim temperatures and ranger work loads caused rangers to be exposed to What Park Employees Can Do excess heat stress and increased their risk of getting heat sickness. A # None of the rangers were acclimatized (used to # Take more time to complete hard work, such as working in the hot weather) and many were not hiking out, by taking longer breaks more often. used to working so hard. A # Wait to do hard work until it’s cooler. A # Every ranger had heat strain, which means that # Soak your body and clothes in the shower or the their heart rates, and/or body temperatures were so creek during hot weather before you leave the high during parts of their work shifts that they were station for rescues or patrol. in danger of becoming seriously ill. A A # Learn to monitor yourselves and co-workers for # Most rangers were mildly dehydrated before and heat stress, and heed the warning signs of heat during their hikes, but none got sick. A stress by taking breaks and rehydrating when needed. # There were not enough rangers to work at inner- A canyon stations when other rangers needed to rest # Take care of personal needs before those of victims or get used to the heat. A for safer, more effective rescues. A # There is no formal heat stress management # Report and record any heat-related illnesses and program at the park. A other concerns. HHE Highlights

What To Do For More Information: We encourage you to read the full report. If you would like a copy, either ask your health and safety representative to make you a copy or call 1-513/841-4252 and ask for HETA Report # 99-0321-2873 Health Hazard Evaluation Report 99-0321-2873

iii U.S. Department of the Interior Grand Canyon National Park Grand Canyon, Arizona April 2002

Ann M. Krake, MS, REHS/RS Joel E. McCullough, MD, MPH Bradley S. King, MPH

SUMMARY

The National Institute for Occupational Safety and Health (NIOSH) received a health hazard evaluation (HHE) request from the management of the Grand Canyon National Park in Arizona. The request indicated that many employees, especially park rangers assigned to the park’s inner canyon and wilderness areas, are at high risk for heat stress illness because duties requiring moderate to extreme physical exertion are conducted in outdoor temperatures that usually exceed 100°F during spring and summer. The requesters asked NIOSH to evaluate heat stress in the work environment and make recommendations to prevent heat illness among the employees.

The first of two investigations was conducted September 5–12, 1999. Core body temperatures (CBTs), physiological hydration measurements, and self-reported heat strain indicators, were collected from patrolling corridor rangers and trail crew personnel rebuilding an inner-canyon section of the North Kaibab trail. The second evaluation took place June 26–July 5, 2000; CBT, heart rate, blood electrolytes, and pre- and post-activity body weights were measured on wilderness and corridor rangers, preventative search and rescue rangers (PSARs), and maintenance rangers. Individual and task-specific metabolic rates were estimated, and wet bulb globe temperatures (WBGTs) were measured during both evaluations. Monitored activities included hiking into and out of the canyon between the South Rim and Phantom Ranch, patrolling the inner canyon, and patrolling the South Rim. Most activities included trail-dependent elevation changes of up to 4,900 feet (ft).

The results were compared to the NIOSH recommended action limits and recommended exposure limits (RALs/RELs) and the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLVs®). NIOSH and ACGIH assess heat stress using sliding scale limits based on environmental and metabolic heat loads. In addition, ACGIH provides physiological heat strain limits in situations of excess heat stress. For individuals with normal cardiac performance, sustained (over several minutes) heart rate should remain below 180 beats per minute (bpm) minus age (in years), maximum CBT should remain below 100.4°F for unselected, unacclimatized personnel (101.3°F for medically selected, acclimatized personnel), recovery heart rate at one minute after a peak work effort should be below 110 bpm, and there should be no symptoms of sudden and severe fatigue, nausea, dizziness, or lightheadedness.

Results of both surveys indicated that most trail crew members and rangers were exposed to heat stress in excess of the screening criteria. During the 2000 survey, daily high WBGTs at Phantom Ranch averaged 92°F with a one- day peak of 98.8°F, and none of the participants could be considered fully acclimatized (used to working in the extreme heat.) All participants experienced heat strain to some degree, i.e., some or all of their measured physiologic parameters exceeded at least one of the evaluation criteria during each activity. Five of six participants hiking out of the canyon exceeded a CBT of 100.4°F an average of 43% of their activities, and two participants exceeded 101.3°F about 20% of the time. One ranger exceeded a CBT of 102.2°F for 14% of the activity, a level that calls for immediate termination of exposure even when the individual is being monitored. All of those hiking out also exceeded the heart rate criterion. All monitored participants hiking into the canyon exceeded the heart rate

iv and CBT criteria, as did five of six PSAR participants patrolling the south rim, and all three employees conducting inner-canyon patrol. All but one of the measured participants developed mild dehydration (body weight loss of 1.5% or less) during their activities in the heat, but their electrolytes remained within normal limits. One case of hypernatremia (attributed to dehydration) occurred. The baseline osmolality (a measure of serum solute concentration) was elevated in approximately 50% of the participants, which indicates some degree of dehydration prior to activities. During both surveys, the majority of employees reported that they had a history of heat-related symptoms or illnesses while working in the park but had never reported them.

Health hazards exist from excessive heat and overwork for employees assigned to the corridor trails and inner canyon of Grand Canyon National Park. Every participant was exposed to combinations of environmental and metabolic heat in excess of occupational criteria, and every participant with heart rate and core body temperature measurements exceeded one or both of the criteria for at least part of the sampling period. The majority of participants reported a history of heat-related symptoms or illnesses while working at the park, however, the park does not have a formal heat stress program for its employees or a system for reporting heat-related illnesses. Recommendations are made regarding reductions in workload and the establishment of work monitoring, heat stress training, and medical surveillance programs.

Keywords: SIC 7999 (Amusement and Recreation Services, Not Elsewhere Classified) and SIC 9512 (Land, Mineral, Wildlife, and Forest Conservation). Heat stress, heat strain, heat-related illness, heat disorders, core body temperature, metabolic rates, WBGT, wet-bulb globe temperature, park rangers, hyponatremia, hypernatremia, dehydration, serum electrolytes, sodium, osmolality.

v TABLE OF CONTENTS

Preface ...... ii

Acknowledgments and Availability of Report ...... ii

HHE Highlights...... iii

Summary...... iv

Introduction ...... 1

Background ...... 1

Methods ...... 2

Evaluation Criteria...... 5

Results ...... 11

Discussion...... 15

Conclusions...... 17

Recommendations...... 17

References...... 20 INTRODUCTION BACKGROUND

On August 18, 1999, the National Institute for The Grand Canyon National Park in Grand Canyon, Occupational Safety and Health (NIOSH) received a Arizona, is one of almost 400 national land areas health hazard evaluation (HHE) request from the managed by the U.S. Department of the Interior’s management of the Grand Canyon National Park, National Park Service. The park includes the South Grand Canyon, Arizona. The request indicated that Rim, which draws 90% of the visitors, the North many employees, especially park rangers assigned to Rim, and the canyon, with the Colorado River the park’s inner canyon and wilderness areas, were flowing through it. The park is 277 river-miles long, believed to be at high risk for heat stress and strain an average of 10 miles wide, about 1 mile in depth, because their duties require moderate to extreme and encompasses 1.8 million acres (1,904 square physical exertion and are conducted in outdoor miles). About 5 million visitors a year to the canyon temperatures that usually exceed 100°F during spring stay an average of 4 hours. and summer months. The requesters asked NIOSH to evaluate heat stress risk in the work environment Access to the inner canyon, Phantom Ranch Lodge, and make recommendations to prevent heat strain and the river, 2,400 feet (ft) in elevation (elev.), is via and illness among the employees. the corridor trail system, the primary work area of concern. The system includes two trails that start at Two investigations were conducted by NIOSH the south rim of the canyon and go to the river, the occupational health and medical officers. During Bright Angel (BA) trail, about 10 miles long, elev. September 5–11, 1999, a preliminary investigation 6,860 ft, and the South Kaibab (SK) trail, about 7 was completed which indicated that park rangers on miles long, elev. 7,260 ft. A third trail, the North inner-canyon patrol and trail crew personnel Kaibab (NK), starts from the canyon’s north rim, rebuilding an inner-canyon section of the North (elev. 8,800 ft), and is about 14 miles long. Each of Kaibab trail were exposed to combinations of the three trails has a change in elevation of about 1 environmental and metabolic heat in excess of mile from beginning to end. Total “rim to rim” NIOSH and the American Conference of mileage (from the south rim down to the river and up Governmental Industrial Hygienists (ACGIH) to the north rim) is about 25 miles, depending upon screening criteria. As a result, a sampling strategy which trails are hiked. Park facilities at Phantom was developed for a more extensive heat stress and Ranch include a ranger station, bunkhouse, strain evaluation during peak hot weather season. wastewater treatment plant, and campground. A similar facility, Indian Garden, is located on the BA During the last week of June and the first week of trail between Phantom Ranch and the south rim, and July 2000, all categories of park rangers, except river another, Cottonwood Camp, is on the NK trail patrol, were evaluated for heat stress and strain while between Phantom Ranch and the north rim. There hiking into and out of the canyon and conducting are no such facilities on the SK trail. Summer other duties. The work environment was assessed temperatures on the south rim range from 50–80°F, with wet bulb globe temperature (WBGT) monitors while north rim temperatures are generally 10°F and by calculating the estimated metabolic heat load cooler. Inner canyon temperatures run about 30°F of each work task. The heat strain evaluation higher than south rim temperatures and have been included monitoring core body temperature (CBT), recorded at 120°F and above. ear temperature, skin temperature, heart rate, activity levels, pre- and post-activity body weights, serum electrolyte analysis, and self-reported heat strain indicators. On August 16, 2000, individual serum analytical results were mailed to participants of that portion of the study.

Health Hazard Evaluation Report No. 99-0321-2873 Page 1 Approximately 400 rangers are employed throughout documented. These rescues and other duties often the park during the summer. They serve in one or require heavy physical exertion and from spring to more of four major job categories—corridor patrol, fall are conducted in temperatures of 100°F and wilderness patrol, river patrol, and interpretation. higher. Fatigue, weight loss, dehydration, and Corridor, wilderness, and river rangers are hyponatremia (water toxicity due to a loss of blood responsible for providing rescue and emergency electrolytes) have been reported among rangers. medical services and law enforcement, and many are Rangers also reported experiencing and observing trained and certified emergency medical technicians co-workers with a lack of coordination, impaired and law enforcement officials. Much of their time is judgement (for example, the inability to make simple spent patrolling the main corridor trails and drug-dosage calculations), and loss of composure campgrounds (corridor rangers), smaller trails and during rescue situations in elevated temperatures. back country campgrounds (wilderness rangers), and the river and river trails (river patrol rangers). Interpretation rangers are responsible for guiding METHODS nature hikes and providing interpretive and educational programs to visitors. There are also Environmental rangers who operate and maintain the wastewater treatment plants throughout the park and who remain During both evaluations, wet bulb globe temperature at their stations while on duty. A fifth category, measurements (WBGTs) were collected using two preventive search and rescue rangers (PSARs), are RSS-214 WiBGeT® instruments (Imaging & Sensing mostly volunteers who work part-time shifts and Technology, Horseheads, New York). These patrol much of the rim area and upper 3 to 5 miles of monitors are capable of measuring temperatures of the BA and SK trails. 32–150°F and are accurate to within ±0.5°F. The WBGT index accounts for air velocity, temperature, Rangers who work the inner-canyon trails stay as humidity, and radiant heat and is a useful index of residents of Phantom Ranch, Indian Garden, or the environmental contribution to heat stress. It is a Cottonwood Camp ranger station for about eight function of dry bulb temperature (a standard measure days while they conduct their duties. The first and of air temperature taken with a thermometer), a last days of each shift are for hiking into and out of natural wet bulb temperature (simulates the effects of the canyon. During the summer, there are nine evaporative cooling), and a black globe temperature, ranger positions that rotate between these three inner- which estimates radiant (infrared) heat load. During canyon locations. However, currently and in the past the 1999 evaluation, environmental conditions on the several years, only six rangers have been available to NK trail were monitored, and for the 2000 cover them—two rangers rotate through Indian evaluation, one WBGT monitor was placed on the Garden and four through Phantom Ranch. There south rim near the ranger headquarters building were no rangers assigned to Cottonwood Camp at the while the other was placed outside the Phantom time of the NIOSH survey. Two maintenance Ranch ranger station. WBGTs were measured at rangers rotate through Indian Garden and Phantom one-minute intervals from morning to late afternoon. Ranch, and one is stationed at Roaring Springs on the NK trail. Individual metabolic rates were estimated using the NIOSH table, “Estimated metabolic heat production Park employees conduct over 2,000 visitor rescues rates by task analysis” (Appendix A). This method per year, most of which involve heat-related allows for specific rate estimation because it breaks illnesses. About 400–500 of these are documented the job down into three categories that account for search and rescue operations, and usually involve body position and movement, type of work, and helicopter evacuation from the canyon, mostly from basal metabolism. Metabolic rates for those on rim Phantom Ranch. Other rescues include hiker assists and canyon patrol were estimated by assuming that and minor medical treatment and are not participants spent approximately two-thirds of the

Page 2 Health Hazard Evaluation Report No. 99-0321-2873 total activity ascending the trail and one-third battery, weighs about 7 ounces, and attaches to the descending or walking on the flat. Each employee’s user’s belt. The rangers’ CBTs were recorded at body weight and estimated pack weight were added 1-minute intervals during each work activity. together and used to calculate a correction factor for the standard weight of 154 pounds (lbs) used in the During the 2000 evaluation, heat strain was also NIOSH table. Estimated pack weights are as assessed using a Mini-Mitter Mini-Logger® Series follows: Law enforcement and life support rangers 2000 (Mini-Mitter Company, Inc., Bend, Oregon). (from all categories), 40 lbs; life support rangers, 30 Heart rate, gross motor activity, skin temperature, lbs; maintenance employees, 20 lbs; and PSARs, 15 and ear temperature, all of which directly impact or lbs. Appendix A includes sample metabolic rate are a function of the body’s metabolic rate, were calculations for rangers who hiked out of and into the monitored at 1-minute intervals.a The participants canyon, calculations ‘1’ and ‘2’, respectively. were asked to wear an aural (ear) temperature probe, a skin temperature probe, Polar® chest band heart rate Metabolic rates for many uphill hikes in the Grand monitor, and an activity sensor on the dominant Canyon were estimated for various completion times ankle. The Mini-Logger’s ear and skin temperature using the same formula as for individuals. Sample readings are accurate to within ±0.18°F and have a calculation ‘3’ in Appendix A provides an example range of 86–108°F. The Polar chest band heart rate of estimating metabolic rates for hiking out of the monitor counts up to 250 beats per minute (bpm) and canyon on the SK trail in 4 hours and 5½ hours, is accurate to within ±1 heart beat. The activity respectively. The information provided is for monitor, which works by counting the number of guidance purposes only, and it is important to note movements per collection interval, is accurate to that individual results will vary depending on age, within ±1 millisecond and counts up to 65,353 sex, fitness level, current health status, pack weight, movements per interval. The logger weighs about 4 body weight, etc. ounces and is worn on the user's belt. During both evaluations, heat strain was assessed Medical using the CorTemp™ Wireless Core Body Temperature Monitoring System (HTI Technologies, For both surveys, the medical evaluation consisted of Inc., Palmetto, Florida). The CorTemp Temperature a self-administered questionnaire and a dehydration Sensor, a 0.9 x 0.4 inch silicon-coated electronic assessment. The questionnaire asked participants to device, is swallowed and provides continuous describe methods used to self-monitor health in the monitoring of CBT to within ±0.2°F. The sensor is heat, history of heat-related illnesses, and usual work passed through the gastrointestinal tract and exits the practices. Before and after each activity, participants body at participants’ normal transit time, an average were asked to record information including date, of approximately 72 hours. The sensor, intended for time, base ranger station, activity, activity completion one-time use only, runs on a non-rechargeable silver-oxide battery for a week or longer and utilizes a temperature sensitive crystal which vibrates in a The ear and skin temperature and activity direct proportion to the temperature of the substance measurements are not included in this report. No surrounding it. This vibration creates an evaluation criteria exist for any of these electromagnetic flux (frequency = 262.144 kilohertz) measurements, and ear and skin temperatures are which continuously transmits through the influenced by environmental conditions thereby surrounding substance. A recorder, the CT2000, decreasing their accuracy. Rather, these receives this signal and translates it into digital measurements will be compared to the CBT, heart temperature information, which is then displayed on rate, and WBGT measurements, which do have the unit and stored to memory. The CT2000 established criteria. Grand Canyon management and Recorder monitors temperatures of 50–122°F. The employees will be provided with the results of any recorder operates on one standard 9-volt alkaline future analyses of these measurements.

Health Hazard Evaluation Report No. 99-0321-2873 Page 3 time, type and amount of fluid and food consumed, combined into the “volunteer” group, and inner- pre- and post-activity weights, and any symptoms canyon maintenance workers, Park Service they experienced during the activity. Degree of management, and others assisting with patrolling dehydration was determined by measuring pre- and activities were combined into the “other employees” post-activity body weights. Weight loss (or gain) group. The activity “hike out of the canyon” over a few hours is a reflection of change in included hikes from Phantom Ranch to the south rim extracellular fluid volume and occurs when water is using either the SK or BA trail, “hiking into the lost from sweating and through the respiratory tract. canyon” included hikes from the south rim to Body weight loss of 1.5% or less is indicative of mild Phantom Ranch on either the SK or BA trail, and dehydration, whereas a loss of greater than 1.5% of “patrols” generally included 1.5 to 5-mile hikes of body weight indicates greater risk of heat strain. the inner canyon and rim areas. Seca Travelite™ digital scales, accurate to within ±0.1 lb with a range of up to 330 lbs, were used. All Methods Limitations weights were obtained with participants wearing their uniforms but not shoes, equipment, or packs. Because of mechanical problems, south rim WBGT data are missing for all but two days of the study During the second survey, changes in blood period. The dry bulb data are hourly averaged chemistries that occurred during the participants’ job temperatures recorded by the Park Service for June activities were also determined. Blood chemistries, 29-July 4, 2000, so peak temperatures are not including sodium, potassium, chloride, blood urea included. The NIOSH monitors collected WBGTs nitrogen (BUN), and glucose were measured to from mid-morning to early evening, and included the determine if levels were maintained within normal highest daily temperature but not the lowest. limits during work activities. Dehydration results in an increase in certain blood chemistries, and Treadmill studies have shown that descents involve hyperhydration (fluid overload) results in a decrease. about 25% less energy than walking on the level; Euhydration, the normal hydration state, results in however, on very steep, slow descents, energy little change. Blood chemistry levels were measured expenditure may be considerably higher than when before participants began their duties and again walking on the level.4 No specific descent afterward, and were determined using the i-STAT adjustment factors exist, however, nor do any of the handheld analyzer and the i-STAT EC8+ cartridges. available methods for calculating metabolic energy (The i-STAT system has been shown to be accurate expenditure include such a provision.5 Therefore, for the blood chemistries it measures, is simple to although calculations for uphill climbs in this study operate,1 and has been used successfully to study factor in an additional 0.8 kcal/min per meter risen hyponatremia among back-country hikers at the (Appendix A), the estimated metabolic rates for Grand Canyon National Park.2) Whole blood (65–95 those who descended do not include any metabolic micro liters [µL]) was placed in the well of the rate adjustment and are likely underestimated. cartridge prior to inserting the cartridge into the analyzer. Serum osmolality (dissolved particle When estimating the metabolic rate for a person concentration in blood) is measured in milliosmols completing a certain task, ideally every move would per liter (mosm/L) and was calculated from the blood be recorded and rates and times would be combined chemistries using the following formula:3 to provide a time-weighted average. The logistics of

Osmolality = (1.86 × serum sodium) + (serum glucose ÷ 18) + (BUN ÷ 2.8) this study were such that participants could not be monitored in this way, and so the metabolic rate For analysis of the second survey results, corridor results may either over- or underestimate the actual patrol rangers, wilderness rangers, and interpretation energy expenditure of each participant. Also, in part rangers were combined into one group called “park because of individual variability, errors in estimating 10 rangers,” PSARs and all other volunteers were metabolic rates may vary by ± 10–15%.

Page 4 Health Hazard Evaluation Report No. 99-0321-2873 Some of the baseline blood samples, although ideally STEL, an employer is still required by OSHA to collected just before the participants begin their protect employees from these hazards. activities, had to be collected hours or even the night before the activity. Thus the change in concentration Heat Stress of the analytes may underestimate the actual changes that occurred during the activity. Also, many Total heat stress is defined by NIOSH as the sum of participants wore clothing that was soaked with the heat generated in the body (metabolic heat) plus sweat during post-activity weigh-ins, likely resulting the heat gained from the environment (environmental in an overestimation of body weight and subsequent heat) minus the heat lost from the body to the underestimation of the actual change in body weight. environment, which is primarily through evaporation. Many bodily responses to heat stress EVALUATION CRITERIA are desirable and beneficial because they help regulate internal temperature and, in situations of appropriate repeated exposure, help the body adapt To assess the hazards posed by workplace exposures, (acclimate) to the work environment. However, at NIOSH investigators use a variety of environmental some stage of heat stress, the body’s compensatory evaluation criteria for the assessment of chemical and measures cannot maintain internal body temperature physical agents. These criteria are intended to at the level required for normal functioning. As a suggest levels at which most workers may be result, the risk of heat-induced illnesses, disorders, exposed for a working lifetime without experiencing and accidents substantially increases.10 Increases in adverse health effects. However, wide variations in unsafe behavior are also seen as the level of physical individual susceptibility may cause a small work of the job increases.10 percentage of workers to experience illness even if exposures are maintained below these levels. The Many heat stress guidelines have been developed to criteria do not account for individual sensitivity, pre- protect people against heat-related illnesses. The existing medical conditions, medications, or possible objective of any heat stress index is to prevent a interactions with other workplace agents. person's CBT from rising excessively. The World Health Organization concluded that “it is inadvisable The primary sources of environmental evaluation for CBT to exceed 38°C (100.4°F) or for oral criteria for the workplace are NIOSH Recommended temperature to exceed 37.5°C (99.5°F) in prolonged Exposure Limits (RELs),6 the American Conference daily exposure to heavy work and/or of Governmental Industrial Hygienists’ (ACGIH) heat.”9 According to NIOSH, a deep body Threshold Limit Values (TLVs),7 and the U.S. temperature of 39°C (102.2°F) should be considered Department of Labor, Occupational Safety and reason to terminate exposure even when deep body Health Administration (OSHA) Permissible temperature is being monitored.10 This does not Exposure Limits (PELs).8 Employers are mean that a worker with a CBT exceeding those encouraged to follow the OSHA limits, the NIOSH levels will necessarily experience adverse health RELs, and the ACGIH TLVs, or whichever are the effects; however, the number of accidents increases more protective criteria. OSHA requires an as does the risk of developing heat stress illness.10 employer to furnish employees a place of employment that is free from recognized hazards that NIOSH recommends that total heat exposure be are causing or are likely to cause death or serious controlled so that unprotected healthy workers who physical harm (Occupational Safety and Health Act are medically and physically fit for their required of 1970, Public Law 91-596, sec. 5(a)(1)). level of activity and are wearing, at most, long- Employers should also understand that not all sleeved work shirts and trousers or equivalent, are hazardous exposures, including heat stress, have not exposed to metabolic and environmental heat specific OSHA PELs or short-term exposure limits combinations exceeding the applicable NIOSH (STELs); however, even in the absence of a PEL or criteria, as follows: Almost all healthy employees,

Health Hazard Evaluation Report No. 99-0321-2873 Page 5 working in hot environments and exposed to suits or garments that are impermeable or highly combinations of environmental and metabolic heat resistant to water vapor or air movement are worn. less than the NIOSH Recommended Action Limits Further assumptions regarding work demands (RAL’s) for non-acclimatized workers (Appendix B, include an 8-hour work day, 5-day work week, two Figure 1) or the NIOSH Recommended Exposure 15-minute breaks, and a 30-minute lunch break, with Limits (REL’s) for acclimatized workers (Appendix rest area temperatures the same as, or less than, those B, Figure 2), should be able to tolerate total heat in work areas, and “at least some air movement.” It stress without substantially increasing their risk of must be stressed that NIOSH and ACGIH guidelines incurring acute adverse health effects. Also, no do not establish a fine line between safe and employee should be exposed to metabolic and dangerous levels but require professional judgement environmental heat combinations exceeding the and a heat stress management program to ensure applicable Ceiling Limits (C) of Figures 1 or 2 protection in each situation. without being provided with and properly using appropriate and adequate heat-protective clothing OSHA does not have a specific heat stress standard, and equipment.10 however, acceptable exposure to heat stress is enforced by the Secretary of Labor under the General ACGIH guidelines require the use of a decision- Duty Clause [section 5(a)(1)].11 The OSHA making process which provides step-by-step technical manual, Section III, Chapter 4,13 provides situation-dependent instructions that factor in investigation guidelines that approximate those clothing insulation values and physiological found in ACGIH’s 1992-1993 Threshold Limit evaluation of heat strain (see Evaluation Scheme for Values for Chemical Substances and Physical Agents Heat Stress, Appendix C). ACGIH WBGT and Biological Exposure Indices. screening criteria (Appendix D) factor in the ability of the body to cool itself (clothing insulation value, Heat Strain humidity, wind), and, like the NIOSH criteria, can be used to develop work/rest regimens for acclimatized The body’s response to total heat stress is called heat and unacclimatized employees. The ACGIH strain.10 Operations involving high air temperatures, WBGT-based heat exposure assessment was radiant heat sources, high humidity, direct physical developed for a traditional work uniform of long- contact with hot objects, and strenuous physical sleeved shirt and pants, and represents conditions activities all have a high potential for inducing heat under which it is believed that nearly all adequately strain in employees. Physiological monitoring for hydrated, unmedicated, healthy workers may be heat strain becomes necessary when impermeable repeatedly exposed without adverse health effects. clothing is worn, when heat stress screening criteria Clothing insulation values and the appropriate are exceeded, or when data from a detailed analysis WBGT adjustments, as well descriptors of the other (such as the International Standards Organization decision-making process components can be found in [ISO] required sweat rate [SR ]) shows excess heat ACGIH’s Threshold Limit Values (TLVs®) for req stress.14 Chemical Substances and Physical Agents and Biological Exposure Indicies.7 The ACGIH TLV for heat stress provides a framework for the control of heat-related disorders only. Although accidents and injuries can increase with increasing levels of heat stress, it’s important to note that the TLVs are not directed toward controlling these.14

NIOSH and ACGIH criteria can only be used when WBGT data for the immediate work area are available and must not be used when encapsulating

Page 6 Health Hazard Evaluation Report No. 99-0321-2873 One indicator of physiological strain, sustained peak Health Effects of Exposure to heart rate, is considered by ACGIH to be the best sign of acute, high-level exposure to heat stress. Hot Environments Sustained peak heart rate, defined by ACGIH as 180 beats per minute (bpm) minus an individual’s age, is Heat disorders and health effects of individuals exposed a leading indicator that thermal regulatory control to hot working environments include (in increasing may not be adequate and that increases in CBTs order of severity) skin disorders (heat rash, hives, etc.), have, or will soon, occur. Sustained peak heart rate heat syncope (fainting), heat cramps, heat exhaustion, represents an equivalent cardiovascular demand of and heat stroke. Heat syncope (fainting) results from about 75% of maximum aerobic capacity. During an blood flow being directed to the skin for cooling, 8-hour work shift, although sustained peak demands resulting in decreased supply to the brain, and most may not occur, there may still be excessive demand often strikes workers who stand in place for extended placed on the cardiovascular system. These periods in hot environments. Heat cramps, caused by ‘chronic’ demands can be measured by calculating sodium depletion due to sweating, typically occur in the the average heart rate over the shift. Decreases in muscles employed in strenuous work. Heat cramps and physical job performance have been observed when syncope often accompany heat exhaustion, or weakness, the average heart rate exceeds 115 bpm over the fatigue, confusion, nausea, and other symptoms that entire shift. This level is equivalent to working at generally prevent a return to work for at least 24 hours. roughly 35% of maximum aerobic capacity, a level The dehydration, sodium loss, and elevated CBT (above sustainable for 8 hours.14 100.4°F) of heat exhaustion are usually due to individuals performing strenuous work in hot conditions According to ACGIH, an individual’s heat stress with inadequate water and electrolyte intake. Heat exposure should be discontinued when any of the exhaustion may lead to heat stroke if the patient is not following excessive heat strain indicators occur: quickly cooled and re-hydrated.

< Sustained (over several minutes) heart rate is in While heat exhaustion victims continue to sweat as their excess of 180 bpm minus the individual’s age in bodies struggle to stay cool, heat stroke victims cease to years, (180 bpm - age) for those with normal sweat as their bodies fail to maintain an appropriate core cardiac performance; temperature. Heat stroke occurs when hard work, hot < Core body temperature is greater than 38.0°C environment, and dehydration overload the body’s (100.4°F) for unselected, unacclimatized capacity to cool itself. This thermal regulatory failure personnel and greater than 38.5°C (101.3°F) for (heat stroke) is a life-threatening emergency requiring medically fit, heat-acclimatized personnel; immediate medical attention. Signs and symptoms < Recovery heart rate at 1 minute after a peak include irritability, confusion, nausea, convulsions or work effort exceeds 110 bpm; or unconsciousness, hot dry skin, and a CBT above 106°F. < There are symptoms of sudden and severe Death can result from damage to the brain, heart, liver, fatigue, nausea, dizziness, or lightheadedness. or kidneys.12

An individual may be at greater risk of heat strain if: Prolonged increases in CBT and chronic exposures to high levels of heat stress are associated with disorders < Profuse sweating is sustained over several such as temporary infertility (male and female), elevated hours; or heart rate, sleep disturbance, fatigue, and irritability. < Weight loss over a shift is greater than 1.5% of During the first trimester of pregnancy, a sustained CBT body weight; or greater than 102.2°F may endanger the fetus.7 In < 24-hour urinary sodium excretion is less than addition, one or more occurrences of heat-induced 55 millimoles. illness in a person predisposes him/her to subsequent injuries and can result in temporary or permanent loss of that person’s ability to tolerate heat stress.10, 13

Health Hazard Evaluation Report No. 99-0321-2873 Page 7 The level of heat stress at which excessive heat strain substantially improve comfort and safety for those who will result is highly individual and depends upon the are in general good health. Exposure to heat only, heat tolerance capabilities of each individual. Age, however, will not bring about acclimatization—an weight, degree of physical fitness, degree of elevated metabolic rate, such as happens during work acclimatization, metabolism, use of alcohol or drugs, activities, is required. The ability of a worker to tolerate and a variety of medical conditions, such as heat stress requires integrity of cardiac, pulmonary, and hypertension and diabetes, all affect a person’s renal function, the sweating mechanism, the body’s fluid sensitivity to heat. At greatest risk are and electrolyte balances, and the central nervous unacclimatized workers, people performing system’s heat-regulatory mechanism. Impairment or physically strenuous work, those with previous heat diminution of any of these functions may interfere with illnesses, the elderly, people with cardiovascular or the worker’s capacity to acclimatize to the heat or to circulatory disorders (diabetes, atherosclerotic perform strenuous work in the heat once acclimatized.10 vascular disease), those taking medications that Acclimatization at a certain temperature is effective only impair the body’s cooling mechanisms,b people who at that temperature—a person exposed to higher levels use alcohol or are recovering from recent use, people of heat stress will not be fully acclimatized at that level, in poor physical condition, and those recovering only the lower one.14 Empirical data suggest that fewer from illness. A core body temperature increase of than 5% of workers cannot adequately acclimatize to only 1.8°F above normal encroaches on the brain’s heat stress.10 ability to function.14 There are three phases of heat acclimatization. Initially, Acclimatization consecutive exposures to heat in the first few days, with the requisite rise in metabolic rate for 2 hours (e.g. doing work, exercising), cause the body to reach 33% of Acclimatization is a low-cost, highly effective way to optimum acclimatization by the fourth day of exposure. improve the safety and comfort of employees in heat The intermediate phase is marked by cardiovascular stress situations.14 Acclimatization allows the stability, and surface and internal body temperatures are employee to withstand heat stress with a reduction in lower, reaching 44% of optimum by day 8. During the heat strain by a series of physiological adaptations. third phase, a decrease in sweat and urine osmolality and Acclimatized individuals are able to perspire more other compensations to conserve body fluids and restore abundantly and more uniformly over their body electrolyte balances are seen, and 65% of optimum is surface and they also start to sweat earlier than non- reached by day 10, 93% by day 18, and 99% by day acclimatized individuals. This results in lower heat 21.14 storage (lower CBT) and lower cardiovascular strain (lower heart rate). In addition, acclimatized Although heat acclimatization for most individuals individuals lose less salt through sweating and are begins early in a period of working in the heat, it is also therefore able to withstand greater water loss.15 quickly lost if the exposure is discontinued. The loss of acclimatization begins when the activity under those Working at even a moderate rate in a heat stress heat stress conditions is discontinued, and a noticeable situation brings about physiological changes that loss occurs after four days. This loss is usually rapidly made up so that by Tuesday workers who were off on the weekend are as well acclimatized as they were on the b –adrenergic receptor blockers and calcium- $ preceding Friday. However, if there is no exposure for channel blockers, used to treat hypertension, limit a week or two, full acclimatization can require up to maximal cardiac output and alter normal vascular three weeks of continued physical activity under heat distribution of blood flow in response to heat stress conditions similar to those anticipated for the exposure. Diuretics, such as caffeine, can limit work.14 Chronic illness, the use or misuse of cardiac output and affect heat tolerance and sweating, pharmacologic agents, a sleep deficit, a suboptimal and antihistamines, phenothiazines, and cyclic nutritional state, or a disturbed water and electrolyte antidepressants impair sweating.10

Page 8 Health Hazard Evaluation Report No. 99-0321-2873 balance may reduce the worker’s capacity to (kcal/min) and as low as 7.3 kcal/min for 55-year-old acclimatize. In addition, an acute episode of mild female workers; in general, older workers have a lower illness, especially if it entails fever, vomiting, capacity than younger workers, and female workers have respiratory impairment, or diarrhea, may cause a lower capacity than male workers.17 With reference to abrupt transient loss of acclimatization.10 a normal, healthy, 35-year-old working man, three limitations in physical work capacity as a function of Workload Assessment working time were proposed by NIOSH in 1981:16 1) an upper energy work limit of 16 kcal/min for 4 minutes; 2) an 8-hour continuous work limit of 5.2 kcal/min (33% of Muscular activity is divided into dynamic exercise 16 kcal/min); and 3) a 24-hour performance limit of (walking, bicycling, etc.) and isometric (static) 2.85 kcal/min, with a female equivalent equal to 70% (of exercise, which involves lifting some form of weight. the values for men). For a general comparison, Dynamic exercise causes greater energy expenditure, estimated hourly metabolic rates for Grand Canyon while static movements readily induce muscular study participants were divided by 60 minutes. fatigue.16 Whole body fatigue occurs when the metabolic demands of dynamic and static activity exceed a worker’s maximum aerobic capacity Fluid and Electrolyte Balance 17 (MAC), or VO2 max. VO2 max varies widely among workers according to age, sex, physical Because water is the most abundant constituent in the fitness, etc.,17 and work capacity is directly body, comprising approximately 60% of the body associated with the number or size of the muscles weight in men and 50% in women, maintaining enough available to do the work.18 A very fit individual can water improves the body’s overall function. Total body sustain higher workloads, averaging about 50% of water is distributed in two major compartments: MAC during an 8-hour shift, however, few industrial 55–75% is intracellular fluid (ICF), and 25–45% is workers meet these fitness levels, so a value of 33% extracellular fluid (ECF).21 The solute, or dissolved is found to be a more appropriate upper limit for particle concentration of a fluid, is known as its them.19 Also, studies show that healthy workers will osmolality (expressed as milliosmoles per liter choose a level of work that produces an average [mosmol/L]). The major ECF component is sodium heart rate of 112 bpm, which is equivalent to 33% of (Na+); therefore, ECF volume is a reflection of total 16 + MAC. Because worker populations, VO2 max body Na content. Normal regulatory mechanisms values, and job conditions vary widely, it is ensure that Na+ loss balances Na+ gain. important to know the VO2 max of individuals or groups of individuals and to avoid prolonged work at Normal plasma osmolality ranges from levels greater than 50% of VO2 max in order to avoid 275–290 mosmol/L and is kept within a narrow range by fatigue.17 mechanisms capable of sensing a 1–2% change in plasma concentration. Most people have an obligate Except for lifting tasks,20 no specific workload water loss consisting of urine, stool, and evaporation standards exist. However, metabolic research from the skin and respiratory tract, and to maintain a findings can provide rough guidelines for steady state, water intake must equal water excretion. establishing appropriate limits for specific worker Disorders of water regulation result in hypo- or populations. Oxygen consumption, metabolic energy hypernatremia. Changes in urine and plasma osmolality expenditure rate, and heart rate are the physiological are better suited for diagnosing hydration status than measurements which have been suggested for changes in hematocrit, serum proteins, and blood urea determining the maximum work intensity that can be nitrogen (BUN), which are more dependent on factors continuously performed without accumulating other than hydration.3 The primary stimulus for water 16 excessive physical fatigue. Average VO2 max ingestion is thirst, mediated by either an increase in values, assessed using treadmill procedures, have effective osmolality or a decrease in ECF volume or been reported for 20-year-old conditioned male blood pressure. Osmoreceptors in the hypothalamus are workers to be as high as 20 kilocalories per minute stimulated by a rise in serum concentration. The average

Health Hazard Evaluation Report No. 99-0321-2873 Page 9 osmotic threshold for thirst is approximately secondary to extensive over-drinking. Many people 295 mosmol/kg and varies among individuals. with hyponatremia have increased their total body water Under normal circumstances, daily water intake by about 1 gallon to achieve such low serum sodium exceeds physiological requirements.22 values.28 Hyponatremia The pathophysiology is complex and probably involves fluid, electrolyte, and plasma protein imbalances between intra- and extracellular Sweat is a hypotonic fluid that contains 10–90 milli- compartments.29 Circulating factors that may be equivalents per liter (mEq/L) of sodium, equal elevated during exercise in the heat include aldosterone, amounts of chloride, and 3–5 mEq/L of potassium. arginine vasopressin (also known as antidiuretic Sustained sweat volumes of 1–2 liters per hour (L/hr) hormone [ADH]), and atrial natriuretic peptide; these are common during strenuous exercise in the have been implicated in the pathophysiology of heat.23 A sweat loss of 1.5 L/hr for 8 hours, with hyponatremia and volume overload. Since elevation of 50 mEq/L of sodium, results in a loss of 600 mEq ADH occurs with exercise and possibly with the initial (26 grams) of sodium. A 154 lb person has plasma expansion that also occurs during exercise, some extracellular sodium stores of 5,880 mEq have ascribed the fluid overload to the ‘syndrome of (264 grams). With no sodium intake, the loss of inappropriate secretion of ADH,’ or SIADH; however, 26 grams of sodium (over 8 hours) would lower the other forms of SIADH require several days to develop, serum sodium to 125 mEq/L. Further dilution could whereas this syndrome occurs in several hours.30 occur if there was excess intake of water.

Hyponatremia develops when serum sodium levels Dehydration and Fluid drop below 135 mEq/L and is a condition that has Replacement been recognized as a potential health consequence of endurance activities conducted in hot environments. When working in hot environments it is often difficult to Most individuals with acute exercise-induced heat completely replace lost fluids as the day’s work illness are dehydrated with normal to mildly proceeds. High sweat rates with excessive loss of body increased serum sodium and serum fluids may result in dehydration and electrolyte osmolality.24 However, decreased concentration of imbalances.31 Some studies have shown that even small sodium in the serum (hyponatremia) has been deficits have adverse effects on performance.32 During recognized as an increasing problem among hikers in the process of dehydration, water is lost from the plasma Grand Canyon National Park.25 more rapidly than from other compartments.33 During more severe dehydration, both the intracellular and Most cases of hyponatremia result from the inability extracellular compartments may be depleted. Changes of the kidneys to excrete an appropriately dilute in both compartments are associated with thirst and urine. The most significant clinical symptoms of drinking. Dehydration also negates the advantage hyponatremia involve the central nervous system, granted by high levels of aerobic fitness and heat and symptoms vary from subtle changes in one’s acclimatization.34 ability to think, to decreases in energy levels, to severe alterations, such as coma or seizure. Several studies have shown that dehydration increases Symptoms generally parallel the rate of development CBT during exercise in temperate and hot and degree of hyponatremia.26 environments; a deficit of only 1% of body weight increases CBT during exercise. As the magnitude of the Hyponatremia may occur with hypo-, hyper-, or water deficit increases, there is an accompanying normal hydration status.27 Symptomatic elevation in CBT when exercising in the heat. The hyponatremia can occur when blood sodium magnitude of this elevation ranges from 0.2–0.4°F concentrations decrease to less than 130 mEq/L and (0.1–0.23°C) for every 1% body weight loss.35 A 2% is generally caused by hypervolemia (water overload)

Page 10 Health Hazard Evaluation Report No. 99-0321-2873 loss of body weight is generally accepted as the common heat-related health problem was the threshold for thirst stimulation.36 A 3% decrease in dehydration they said usually occurs during strenuous body weight causes an increase in heart rate, duties, especially victim rescues. The rangers described depressed sweating sensitivity, and a substantial rescue situations where they found themselves in decrease in physical work capacity.37 Some isolated areas with insufficient water and other supplies. investigators have reported that a 4% to 6% water They reported that hiking to and from the rim, deficit has been associated with anorexia, sometimes several times a week, was another activity impatience, and headache, while a 6% to 10% deficit that often results in dehydration and heat strain. Most is associated with vertigo, shortness of breath, mentioned they drank water and glucose-electrolyte cyanosis, and spasticity. With a 12% water deficit, replacement fluids to replace sweat loss. Several trail an individual will be unable to swallow and will need crew members described incidents in which former trail assistance with rehydration. Lethal dehydration crew leaders required employees to continue with their levels are estimated to occur at 15% to 25% lost work, even as they were observed to be developing body weight.38 visible signs of heat strain. NIOSH investigators noted there were current park management policies to help Palatability of any fluid replacement solution is mitigate potential heat strain among trail crew members, important to ensure adequate rehydration. There is including performing trail work in the canyon only evidence that adding sweeteners to drinks leads to during cooler months (with the crews working at or near increased consumption. Glucose-electrolyte the rim in summer) and adjusting the crews’ work solutions have been shown to facilitate sodium and schedules to early morning and late afternoon/early water absorption. Also, the glucose in these evening hours. solutions provides energy for muscular activity in endurance events that require vigorous Workload and Task exercise.39 The temperature of the drink will also influence consumption of fluids. Ideally, fluids Assessments should be ingested at 50–60°F in small quantities (5–7 ounces) and at frequent intervals (every June and July are usually the hottest months at the 15–20 minutes). Grand Canyon, and the temperatures that were measured at Phantom Ranch and on the south rim were typical for that time of year. Daily high WBGTs at RESULTS Phantom Ranch averaged 92°F with a one-day peak of 98.8°F, and for two days of the study, south rim WBGTs During the 1999 survey, estimated individual averaged 78°F (Table 1). Participants wore the uniform metabolic rates ranged from 300 kilocalories per of the U.S. Park Service, which includes short-sleeve hour (kcal/hr) to over 500 kcal/hr, and inner-canyon cotton-blend tan-colored shirts and dark-green shorts, WBGTs averaged 83°F, with a one-day peak of hiking boots, and hats; the PSARs wore shirts that were 98°F. These results indicate that most trail crew dark green and of a thicker cotton-blend material. members and rangers were exposed to excessive heat Therefore, no ACGIH WBGT clothing corrections were stress. While all participants had small to moderate necessary. rises in core temperature, none exceeded the CBT criterion. The median percent body weight loss of The activities of the participants were also typical, trail crew members was 1.5%. One employee lost 6 except that no rescues were conducted. About 60% of pounds (3.0% of body weight). participants’ estimated metabolic rates were between 250 kcal/hr and 400 kcal/hr, while the rest were in the Two park rangers, five trail crew members, and one range of 500–750 kcal/hr. Due to the nature of the job, maintenance employee had confidential interviews none of the participants remained in one location and, with the NIOSH medical officer, and all reported at during their hiking activities, most underwent least one incident in which they had suffered a considerable changes of elevation within short periods of heat-related symptom. Each thought the most time. As a result, they experienced significant air

Health Hazard Evaluation Report No. 99-0321-2873 Page 11 temperature changes, which for practical and their activities when compared to the results of those logistical reasons could not be recorded, therefore who regularly work in the canyon. making heat-stress screening difficult for many Grand Canyon tasks. There were 15 participants in the environmental component of the study including 8 park employees 6 Metabolic rates for a variety of uphill hikes in the park volunteers, and 1 visitor. In all, 21 sets of data Grand Canyon were estimated for various were collected as some rangers completed multiple completion times using the same formula as for tasks. The work schedule for Phantom Ranch, Indian individuals, but without the correction factor (Table Garden, and Cottonwood Camp employees is about 8 2). Most of the estimated rates fell between 300 days of work followed by about 6 days of leave in a kcal/hr and 500 kcal/hr (for 154 lb hiker), depending significantly cooler climate. When work activity in hot upon elevation change and completion time, and are environments is discontinued, a noticeable loss of therefore considered moderate to heavy workloads acclimatization occurs after just 4 days; if there is no (Appendix D). Table 2 also illustrates that exposure for a week or two, full acclimatization can irrespective of environmental temperatures, elevation require up to three weeks of continued physical activity changes and hiking rates can have marked effects on under heat stress conditions similar to those in the work metabolic rate and subsequent heat stress risk and the environment.14 Phantom ranch “regulars,” therefore, are development of heat illness. likely never fully acclimatized to conditions in the canyon, but are at various stages of acclimatization. Individual and task metabolic rate estimates Therefore, according to the criteria, none of the indicated that physical requirements for many Grand participants were considered acclimatized for the Canyon activities exceeded the criteria. At the time purposes of this study. of the study, none of the participants had been medically evaluated for fitness of duty in a hot The results, divided by activity in Tables 3–6, indicate environment, and many, including all of the PSARs, that every monitored participant experienced heat strain had not been medically evaluated for physically to some degree, i.e., the rangers’ measured parameters challenging work. The estimated metabolic rates for exceeded at least one of the heat strain criteria during male and female study participants ranged from each activity. The trails the participants hiked are listed 7.6–12.2 kcal/min for those hiking out, from 4.2–6.6 because of their differences. The SK trail, although kcal/min for those hiking in, from 4.6–7.3 kcal/min approximately 3 miles shorter than the BA trail, is for those on rim patrol, and from 5.1–7.1 kcal/min considered very strenuous and difficult by most rangers for those on inner canyon patrol. because of its steepness, complete lack of water, and little to no shade. The BA trail is about 10 miles long Physiological (Heat Strain) and less steep, with an elevation change of about 400 feet less than the SK trail. The BA trail also has three Monitoring park-maintained water facilities and at least two creeks, and parts of it are shaded. The number of participants and the acclimatization status of the rangers differed in the 2000 NIOSH Only one ranger and four PSARs completed activities survey because of a hiring freeze. The freeze made that lasted approximately 8 hours, while the rest of the it necessary for the Park Service to provide Phantom participants finished their activities in 3–5 hours. Ranch with relief rangers, many of whom were Therefore, only the results for PSARs J, K, M, O, and recruited from south rim automobile patrols and were ranger B, are ‘full-shift’ time-weighted averages. The not used to working in the hot environment at the full-shift averages for the rest of the participants would bottom of the canyon. These relief rangers were likely have been lower but would depend upon the neither medically selected nor required to acclimatize activities of each participant during the rest of the shift. to their new work environment and had the highest CBTs and heart rates over the greatest percentages of

Page 12 Health Hazard Evaluation Report No. 99-0321-2873 The results for those hiking out of the canyon are listed questionnaires, were weighed, and/or had blood drawn in Table 3. Five of six participants completing seven for electrolyte analysis. Two workers completed the activities exceeded the HR criteria of 180 bpm minus questionnaire but did not have their blood drawn or a age, ranging from 11–92% of their activities (one HR body weight measurement. Seventeen workers were monitor failed). Five of the six participants also monitored for one activity, and three workers were exceeded 100.4°F CBT, ranging from 13–70% of monitored for more than one activity. their activities. Two of those rangers, both used to working on the south rim, exceeded 101.3°F CBT The median age of the park rangers was 35 years, the (the criterion for acclimatized workers) for about PSARs, 27 years, and the other employees, 44 years. 20% of their activities, and one had a CBT of The rangers had worked in Grand Canyon National Park 102.2°F for 35 continuous minutes, which is reason a median of 3.5 years, the PSARs, 0.4 years, and the to terminate exposure even when the employee is other employees a median of 4.5 years. Among the being monitored.10 The only ranger who did not eight rangers, four (50%) were women; of nine exceed 100.4°F CBT is a Phantom Ranch “regular” participating PSARs, six (67%) were women; and all who hiked out on the BA trail. five participants in the others category were male.

Table 4 lists the results for participants who hiked Seventeen (77%) of the questionnaire respondents into the canyon except that three of five HR monitors reported monitoring their hydration status while exposed failed as did one CBT monitor. Two participants to work in hot environments. The monitoring methods exceeded the HR criterion from 6.6–15% of their they used included drinking fluids when thirsty, activities. Four participants exceeded 100.4°F CBT monitoring sweat output, monitoring the color of their from 2.6–68% of their activities, and one ranger urine, and weighing themselves before and after exceeded 101.3°F CBT for about 2% of the time. It working in the heat. However, only four individuals should be noted that ranger C3 was returning to (18%), all using personal heart rate monitors, reported Phantom Ranch after having hiked out earlier that monitoring themselves for working too hard in the heat. day (see C1, Table 3), which could contribute to Twenty-two individuals (81%) reported that they had, in increased CBT and HR results. the past, experienced at least one heat-related symptom while on duty, while fifteen (55%) reported two or more Results for participants patrolling the outer heat-related symptoms. Of those reporting single canyon/rim area are listed in Table 5. Five of six symptoms, the most common was fatigue (15%). Thirty participants exceeded the HR criterion 3.5–47% of percent reported that they drank caffeinated or alcoholic their activities, and two of six had HR averages in beverages while off duty and exposed to hot excess of 115 bpm for their entire 9½ hour shifts. All environments. six participants exceeded 100.4°F CBT, and one exceeded 101.3°F CBT. Twenty participants, some completing more than one activity, were monitored for weight change and pre- and Table 6 lists the results for rangers conducting inner- post-shift blood chemistry changes. The activities canyon patrol. Two of three heart rate monitors included 4 hikes into the canyon, 7 hikes out of the failed, but the working monitor indicated that one canyon, and 12 patrols. Most serum electrolyte ranger exceeded the HR criterion for 20% of the concentrations were within normal limits. Five activity. Another ranger exceeded 100.4°F CBT for individuals experienced a decrease, while six had an 36% of the activity and also exceeded 101.3°F CBT increase, in post-activity sodium levels compared to for a short time (1.6%). baseline levels of 135–145 mEq/L. Only two individuals had post-activity sodium out of the normal Medical range; one had a level of 135 mEq/L or lower, and another had a level of 145 mEq/L or greater. Individual weight change results ranged from no change (0%) to - Twenty-two employees and volunteers, including a visitor, a park manager, and seven PSARs, completed

Health Hazard Evaluation Report No. 99-0321-2873 Page 13 2.6%. Individual weight change and blood test dehydration because of greater fluid loss through results for participants are listed in Tables 3–6. increased urine production.

For the three participant groups, the amount of During both surveys, participants expressed concern weight change did not differ (Figure 1). The median about the potential for impaired judgement reportedly percent decrease in body weight for park rangers was brought on not only by heat stress, but also by regularly- 1.3% (range of 0.0–1.9%), 1.2% for the volunteers occurring sleep deficits. They mentioned a hiring freeze (range of -0.9–2.3%), and 1.1% for other employees that has reportedly reduced staff numbers by 40% (range of 0.3–2.6%). The median serum sodium throughout the park. As a result, inner-canyon levels were also similar among the groups, but the employees reported that they have no one to replace park ranger group had much less variability than the them when they need rest after being up all night, are other two groups (Figure 2). A similar finding heat strained, or are becoming acclimatized. Others occurred in the calculated serum osmolality. Most were concerned about the lack of an official supervisor individuals in the groups did not experience at Phantom Ranch, lack of enforcement of employee physiologically significant changes from baseline policies, and poor communication between employees values in the measured blood chemistries (Table 7). and management. Also mentioned was a general lack of support for their efforts in establishing heat stress health For most activities, the median percent weight loss and safety guidelines for park employees. Several was similar (Figure 3), and for all activities, the rangers also mentioned that the “rescue mentality,” median percent loss in body weight was 1.0% or common to many helping professions and including the greater. Hiking out of the canyon was associated ranger/rescue/law enforcement culture, keeps rangers with the greatest median weight loss (1.3%) and also from taking care of their own needs before those of the caused the greatest changes in serum sodium victim in an emergency. The potential for skin cancer concentrations (Figure 4). When grouped by was also a concern, and most of the rangers said they activity, the differences in individual serum sodium regularly wear hats and sunglasses, but less than half concentrations and osmolality changed little between regularly use sun block. baseline and post-activity values (Table 8). In 10 participants (45%), the baseline calculated osmolality The Park Service has no formal policy regarding was greater than 290 mosmol/L (normal range is acclimatization, and all employees and volunteers are 275–290 mosmol/L). There were no significant expected to complete their duties regardless of their changes in glucose, potassium, or chloride between states of acclimatization. Workers are also not screened the different activities. by health care providers to determine if they are at increased risk for heat-related illness. And, while most Interview and Questionnaire participants reported that they had experienced at least one occupationally-related heat illness, there is no Results surveillance system in place, and the incidents went unreported. A few participants monitored their exertion levels using heart rate monitors, which is one of the best methods to determine individual heat strain. Most DISCUSSION participants reported monitoring their hydration status when exposed to hot environments, however, The results of the study confirm that participants many individuals said they used thirst as a gauge to working the corridor trail system, including the south their state of dehydration. Thirst is a poor indicator rim and inner-canyon areas, experienced heat stress of hydration status because significant dehydration exposure resulting from high air temperatures and high has already taken place when the thirst sensation physical workloads. And, though no one developed heat occurs. And, some were unaware that alcohol- and illness during the study, all participants experienced heat caffeine-containing beverages may result in strain at levels that should have triggered a cessation of

Page 14 Health Hazard Evaluation Report No. 99-0321-2873 activity followed by rest and rehydration until their Visitor Rescues CBTs, heart rates, and body fluids had returned to safe levels.10,14 Many of the participants were not Rescue services, while not obligatory, are routinely sufficiently hydrated or rested prior to beginning their performed regardless of staffing levels. Most of the activities, which could have precipitated the onset more than 2000 rescues per year are for victims of and intensity of the heat strain. (preventable) heat-related illness. Rescues may involve long hikes to reach victims, often during the hottest part Lack of acclimatization also was likely an important of the day, sometimes on steep and dangerous terrain, factor in the heat strain experienced by participants. sometimes in the dark, and reportedly many times Corridor and wilderness rangers are never without adequate food, water, or sleep. According to the sufficiently acclimatized because of their work participants, park visitors have unlimited access to the schedules and off-work living conditions in cooler corridor trail system and are not aware of heat stress temperatures. The mostly voluntary PSARs conduct dangers. physically demanding patrols that are scheduled to reflect peak visitor hours, which often occur during Reducing the number of rescues would reduce heat the hottest parts of the day. The patrols require stress incidents among the rangers. One way of descents on the trails into hot environments where achieving this is to require more visitor education prior the PSAR may remain for a few hours but not long to starting down the trail. Currently, back-country enough to become acclimatized. hikers are required to view an educational video prior to obtaining their permits, however some rangers felt that Other factors that likely contributed to participant the video does not provide sufficient guidance on heat heat strain included poor work habits, lack of stress issues. The rangers also believe that all park training, and no fit-for-duty evaluations for work in visitors should receive heat stress education before they hot and physically strenuous work environments. begin their hikes, not just those requiring permits. Heat For example, during the hottest parts of the day, stress warnings and recommendations, in English only, rangers were seen conducting non-essential activities were seen at trail heads, infrequently on the trails, on requiring high metabolic rates, such as hiking out of tent cards in at least two cafeterias, and in the park’s the canyon for leave, lengthy non-essential patrols, newspaper, The Guide. Park administration is in the and post-hole digging. Rangers and PSARs reported process of developing and implementing a restricted- that they were not trained to understand and respond access system where visitors are brought in by train. to heat stress and strain situations in which they This would provide an opportunity to educate visitors on found themselves. Study results indicated that the dangers of hiking the corridor trails and could also be personal monitoring will be especially important for used to limit corridor trail access to those visitors who employees working the corridor trail system are sufficiently educated and prepared. conducting activities that involve changes in elevation or other areas where WBGT data are not Reducing the number of rescues may involve improving available. Heat stress screening, and thus the trail facilities. Hikers on the Bright Angel trail have determination of work/rest regimens, were not found access to at least three drinking water sources and there to be practical for all employees, but could be useful are likely to be PSARs and rangers available to help. for those who stay in the Phantom Ranch and Indian But, because the South Kaibab trail is 3 miles shorter, Garden areas, such as the maintenance rangers, many hikers choose this route instead, believing it to be because both these locations have WBGT monitors. easier. Hikers using the South Kaibab trail, however, do And, given the metabolic rate results, the physical not have access to drinking water or shade, and there are demands of the job, and the wide variety of generally no PSARs or rangers available. On several participant fitness levels, individual VO max testing 2 different days, a NIOSH investigator encountered hikers would likely provide important data for the medical on the South Kaibab trail believed to be in significant evaluation of current and prospective Grand Canyon heat distress. The NIOSH investigator provided water employees and volunteers. and sought out rangers to provide assistance.

Health Hazard Evaluation Report No. 99-0321-2873 Page 15 Heat stress rescues may also be reduced by educating much time, especially in the case of a rescue. Also in visitors on the dehydrating effects of alcoholic and rescue situations, many admitted to being stranded with caffeinated beverages. Guests of Phantom Ranch the victim without adequate food or water because of Lodge and other concessions (not part of the Park poor planning and preparation prior to leaving the Service) are served caffeinated tea and coffee with station. During the survey, most rangers expressed breakfast and dinner and can purchase alcoholic surprise at how their bodies responded to even the beverages, as well. There are no verbal or posted simplest activity as they checked their CBT monitors. warnings to visitors about the dehydrating effects of For example, one ranger reported noticing a big these beverages. difference upon soaking down with water—both CBT and heart rate were decreased, and there was increased Study Observations comfort while hiking. It was evident to us from the physiological results and A specific assessment of the physical impact of the interviews that there are not enough personnel to workload on study participants was not conducted. provide relief to those working at Indian Garden, However, it was observed that those working the Phantom Ranch, and Cottonwood Camp. Employees’ corridor trail system may be at increased risk of heat exposures need to be limited and sufficient rest developing degenerative joint diseases because of breaks provided. Employees may become impaired as their heavy physical workloads and repetitive work 8-hour shifts are extended, especially in hot work activities. One such joint disease is osteoarthritis environments where an increase in CBT of only 1.8°F (OA), a painful, disabling condition of the joints above normal encroaches on the brain’s ability to caused by a gradual deterioration of the cartilage function.14 The rangers reported having to work long between the joints. Continuous stress on joints can hours, sometimes greater than 24 consecutive hours, cause premature breakdown of the cartilage, thus without sufficient time to sleep or rest. Some increasing the likelihood of developing OA. The researchers have found that sleep deprivation may result changes which occur in OA are currently viewed as in decreased reaction time and an increase in perceptual an adaptive response of joints to a variety of genetic, and cognitive distortions and changes in mood.44 Slower constitutional, or biomechanical insults.40 Studies rates of recovery from effort and higher resting heart rate have shown that workers whose jobs involve levels are also associated with fatigue caused by sleep physical labor have high rates of knee OA.41,42,43 loss.45 When jobs with heavy physical labor were examined, those requiring kneeling or squatting along with There are few laws or regulations governing work hours heavy lifting were associated with especially high in the U.S. However, one example of a state regulation rates of both knee and hip OA. Forces across the limiting hours of workers, specifically physicians in knee increase in the crouching or squatting position, training (residents) in New York, is discussed in the Bell and lifting loads from such a position further Commission report.46 The Bell Commission mandates increases loading. Because much of OA may be that residents must work no more than 24 consecutive attributed to modifiable environmental risk factors, hours, must have no less than 8 non-working hours namely occupation, physical activity, quadriceps between shifts, and must not work more than 80 hours strength, joint injury, obesity, and diet, identification per week. The federal government has placed a 10-hour of these factors provides an opportunity to modify or limit on the length of time a long-haul trucker can drive prevent disease. each day, and there are also federal regulations governing flight and rest times for commercial airline Although most of the rangers demonstrated pilots. Research has suggested that work schedules can significant knowledge of heat stress and strain issues, be improved, and a well-designed work schedule can few seemed to follow the guidelines they are helping lead to increased health and safety, worker satisfaction, to develop. For instance, few rangers ever soak and productivity.47 themselves with water before going out on patrol or on a rescue. Many reported that doing so takes too

Page 16 Health Hazard Evaluation Report No. 99-0321-2873 CONCLUSIONS Administrative Controls Regarding Employees Environmental temperature measurements and work load assessments confirmed that there are significant U Reduce the physical demands of the work. Consider health risks to Grand Canyon employees and alternatives such as mule or helicopter transportation, volunteers, especially those working the corridor trail especially for employees leaving the canyon. system during the summer. Also, although relatively few of the participants had major changes in their U Develop and implement a formalized plan to limit fluid and electrolyte measurements, based upon the work hours. Employee representatives and physiological measurements, significant heat strain management should improve the current work/rest was evident. These results justify including schedule for those working both inner- and outer-canyon employees in a formal heat stress management areas. This may involve maintaining a staff of two or program. The fact that few symptoms were reported three mostly-acclimatized workers at the station at all indicates that participants may not have been aware times, one available for nighttime medical emergencies, of their heat strain, indicating a specific need for a one for relief of any unacclimatized ranger who has physiological self-monitoring program. worked in the heat as much as s/he should for the day, and possibly another for injured or ill employees.

U Institute pre-placement and periodic medical examinations of persons applying for work in hot and/or ECOMMENDATIONS physically demanding environments. Because aerobic R capacities (VO2 max values) in the working population vary greatly, persons being considered for jobs requiring An effective heat stress management program is high metabolic demands should be specifically tested. essential to ensuring adequate protection for Only through routine aerobic capacity testing can employees against heat stress and strain. The objective decisions be made about what job is “too following recommendations are provided to help difficult for certain susceptible groups of people and for park management and employees work together to specific individuals.”16 The examination should be create a heat stress management program that will performed by a health care provider with knowledge of reduce the incidence of heat stress and strain among the health effects associated with work in these Grand Canyon National Park employees. environments. The examinations should be performed to assess the physical, mental, and medical qualifications Communication of the individuals and to exclude those with low heat tolerance and/or physical fitness. The health care U To facilitate communication, park management provider should also update the information periodically and employees, especially those who work in the for people working in these environments. canyon and may be under-represented at policy- setting and other meetings, should create health and U Develop a heat-related illness surveillance program, safety committees to discuss specific Phantom which includes establishing and maintaining accurate Ranch/corridor trail work-related health issues. One records of any heat-related illness events and noting the way to begin is to discuss how to reduce the number environmental and work conditions at the time of the of events requiring rescue. Other topics could illness. Such events may include repeated accidents, include establishing acclimitization schedules, episodes of heat-related disorders, or frequent health- developing educational programs such as for skin related absences. Job-specific clustering of specific cancer screening and sun block use, and evaluating events or illnesses should be followed up by the effectiveness and acceptability of ice vests and environmental and personal monitoring and medical other cooling garments. evaluations. A successful program will encourage

Health Hazard Evaluation Report No. 99-0321-2873 Page 17 employee and park volunteer participation, and each should permit self-limitation of exposures.10, 16 Being must understand the reasons for using new, or able to work 100% of the shift does not mean that changing old, work practices for maximum workers will be fully acclimated after 5 days, but that participation. they could work their entire shift in the work environment in which they were acclimatized. The U Develop continuing education programs to ensure body’s acclimatization will continue to improve each that all employees and volunteers potentially exposed day in that environment for up to 3 weeks. Figure 5 to hot environments and physically demanding job illustrates the acclimatization schedule for both types of activities stay current on heat stress and heat-stress workers. prevention information. Include at least the following components for a good heat stress training U Because Grand Canyon rangers, PSARs, and others program: will be exposed to WBGTs and/or physically demanding work rates which exceed recommended < knowledge of the hazards of heat stress; levels, they should be instructed on personal monitoring < recognition of predisposing factors, danger signs, techniques. Personal monitoring is used in addition to and symptoms; environmental and metabolic monitoring, and involves < awareness of signs and symptoms of heat-related checking the heart rate, oral temperature, extent of body illness and first-aid procedures for treatment; weight loss, and/or recovery heart rate (see Appendix E). < employee responsibilities in avoiding heat stress; Measurements should be taken at appropriate intervals < dangers in using drugs, including therapeutic covering a full 2-hour period during the hottest parts of ones, and alcohol in hot and physically the day, and again at the end of the workday to ensure a demanding work environments; return to baseline.10 Use of any of these techniques < use of protective clothing and equipment and the should always include the determination of baseline potential for increased heat stress risk; values for deciding whether individuals are fit to < purpose and coverage of environmental and continue work that day. medical surveillance programs and the advantages of worker participation in them. U Install an outside shower at each station for rangers to soak themselves and their clothing prior to outdoor U Establish a heat-acclimatization program. One activities. In conditions of high temperature and low that is properly designed and applied will humidity, where evaporation from garments is not dramatically increase the safety of workers in hot and restricted, wetting clothing is a very simple and physically demanding jobs and will decrease the risk inexpensive personal cooling technique and should be of heat-related illnesses and unsafe acts. Such a mandatory prior to any activities in the heat. program involves having employees work in hot environments for progressively longer periods. U Provide accurate scales at each work station to enable NIOSH recommends that workers who have had employees to monitor their body weight, and thus previous experience in jobs where heat levels are hydration status, prior to and after work that is high enough to produce heat stress (CBT and heart physically demanding and/or conducted in a hot rate increase but do not exceed recommended levels) environment. should work in the environment 50% of the shift on day one, 60% on day two, 80% on day three, and U Assign the PSARs shirts that are lighter in 100% on day four. New workers who will be color/more reflective than their dark green ones. similarly exposed should start with 20% on day one, with a 20% increase in exposure each additional U Consider the use of commercially available ice vests. day.10 Because employees who have worked at Ice vests may be appropriate for many Grand Canyon Phantom Ranch, Indian Garden, and Cottonwood job activities. They accommodate as many as 72 small Camp regularly for many months would likely fall ice packs and cooling lasts 2–4 hours at moderate to somewhere between the two schedules, the program heavy heat loads. Cooling with ice is relatively

Page 18 Health Hazard Evaluation Report No. 99-0321-2873 inexpensive, and the vest is generally not U Schedule physically demanding jobs for the cooler cumbersome and permits high mobility. However part of the day, and schedule routine maintenance and the weight of the vest and ice must be added to the repair work in hot areas during cooler seasons of the employee’s pack weight for the correction factor year. When temperatures are highest, restrict patrol to when metabolic rates are estimated prior to outside immediate areas (e.g. the campground). Delay response activities. to minor mishaps, if status is known, until temperatures have cooled. U Encourage all employees to carry cool (50–60°F) water or any cool liquid (except alcohol and U Use the attached metabolic rate chart (Table 2) prior caffeinated beverages) and to drink small amounts to heading out to choose trails and completion times that frequently, e.g., one cup every 20 minutes. suit your individual needs and anticipated environmental conditions. Begin by calculating your individual weight correction factor to get your estimated metabolic rate (see Appendix A, sample calculation 1 for Administrative Controls an example). The estimated rates in Table 2 must be multiplied by your correction factor for a more accurate Regarding Visitors metabolic rate estimate for that hike. For example, if your body and pack weight combined are less than 154 U Educate visitors prior to their hiking activities to lbs, the estimated metabolic rate will be less than that protect them from heat illness and reduce the need for listed in Table 2, and if your combined weight is greater rescue services. Such education might include than 154 lbs, the estimated metabolic rate will be higher. stationing a ranger or volunteer at each trail head to WBGTs (if known) should be used to assess heat stress assess the status of hikers who attempt access and/or risk prior to beginning any of the hikes. having a mandatory video viewing at the trail head. U If you will be working in a fixed location, i.e., U Translate all warnings and recommendations into Phantom Ranch or Indian Garden, check the WBGT languages that reflect the diversity of the park’s monitor every 45 minutes or so noting any temperature visitors. changes. Use your calculated metabolic rate and the WBGTs for comparison to either the NIOSH or ACGIH U Consider adding water stations or maintaining figures (Appendices B and D) to see how frequently you water caches on the South Kaibab trail. More water should take breaks. If your calculated metabolic rate stations overall, but especially on the SK trail, should and/or the WBGTs are too high to register on the charts, reduce the need for rescues and help rangers in heat wait until temperatures have cooled, or increase the distress, as well. amount of time you take to complete the activity, and see Appendix E for personal monitoring instructions. U Consider placing emergency radios at appropriate intervals along all trails for earlier reports of visitors U Carefully monitor your coworkers for signs of heat in distress. illness and for adequate supplies when leaving for rescues or other emergencies. Creating a ‘buddy’ Employee Practices and Heat system among rangers in the canyon will help to ensure that each of the rangers has enough water and food and Strain Monitoring has soaked down prior to leaving. If a co-worker shows signs of heat intolerance (weakness, unsteady gait, U Take more time to complete activities that have irritability, disorientation, confusion, changes in skin uphill climbs associated with them by taking longer color, flu-like symptoms, or general malaise) the worker and more frequent breaks. should rest in a cool location with rapidly circulating air and be kept under skilled observation. Immediate emergency care may be necessary. If sweating stops and

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Page 22 Health Hazard Evaluation Report No. 99-0321-2873 Table 1: WBGT Environmental Temperature Data Grand Canyon National Park, HETA 99-0321-2873

Date WBGT Range Sampling Times WBGT Range Sampling Times Phantom Ranch (Time of Highest Temp.) South Rim (Time of Highest Temp.) 6/27/00 65.8-90.9°F 08:50 - 17:19 (15:15) 62.8-76.1°F 11:34 - 20:03 (13:11) 6/28/00 73.8-93.2°F 11:25 - 19:54 (16:42) 61.2-79.2°F 11:12 - 19:41 (14:45) 6/29/00 75.7-92.5°F 12:24 - 20:53 (14:59) )) 6/30/00 70.9-92.3°F 11:14 - 19:43 (16:48) )) 7/01/00 69.8-93.0°F 11:58 - 20:27 (16:44) )) 7/02/00 68.5-88.3°F 11:47 - 20:16 (17:37) )) 7/03/00 62.4-86.9°F 10:24 - 18:53 (17:54) )) )) 7/04/00 70.0-98.8°F 13:56 - 20:53 (16:42) ) Data not available because of equipment failure.

Date Dry-Bulb Range Sampling Times Dry-Bulb Range Sampling Times Phantom Ranch (Time of Highest Temp.) South Rim (Time of Highest Temp.) 6/27/00 74.3-111.2°F 08:50 - 17:19 (17:11) 72.7-88.5°F 11:34 - 20:03 (18:29) 6/28/00 69.4-114.8°F 11:25 - 19:54 (16:42) 70.7-93.0°F 11:12 - 19:41 (14:64) 6/29/00 90.9-108.9°F 12:24 - 20:53 (14:46) ,60.3-77.0°F 00:00 - 23:00 (11:00) 6/30/00 83.1-109.9°F 11:14 - 19:43 (16:48) ,60.8-78.3°F 00:00 - 23:00 (17:00) 7/01/00 83.5-114.4°F 11:58 - 20:27 (18:29) ,59.2-82.2°F 00:00 - 23:00 (14:00) 7/02/00 82.6-111.7°F 11:47 - 20:16 (17:36) ,55.8-79.5°F 00:00 - 23:00 (14:00) 7/03/00 72.9-110.5°F 10:24 - 18:53 (17:52) ,55.8-79.7°F 00:00 - 23:00 (14:00) 7/04/00 92.3-122.5°F 13:56 - 20:53 (16:41) ,51.8-79.7°F 00:00 - 23:00 (14:00) , These measurements were collected by Grand Canyon National Park temperature monitors.

Health Hazard Evaluation Report No. 99-0321-2873 Page 23 Table 2: Estimated Metabolic Rates for Various Completion Times (kilocalories per hour [kcal/hr]), without Correction Factors,* for Uphill Hiking Activities Grand Canyon National Park, HETA 99-0321-2873

n n- io o t ge** ati ca n s c o ** a te o L e h u s s s s s s s s L g C in r urs r urs r urs r urs r urs r urs r urs r urs r il t ea . u o u o u o u o u o u o u o u o u a ar il m r t inish lev 0 ho ½ h ho ½ h ho ½ h ho ½ h ho ½ h ho ½ h ho ½ h ho T S F M E 3 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8½ h 9 ho

Colorado River-South Rim 10 1359 784 675 602 551 512 481 457 437 421 407 395 385 376

Colorado River-Pipe Creek Rest House 1.5 49 318 279 266 260 256 253 * These metabolic rates (MRs) have NOT been corrected for Colorado River-Devil’s Corkscrew 3 114 422 331 301 286 277 270 body and pack weight. Use the Colorado River-Indian Garden 4.5 450 480 420 384 360 343 330 320 312 formula below to calculate an individual correction factor Indian Garden-South Rim 4.5 933 613 538 489 453 427 406 389 376 364 355 (CF) then multiply the CF by the MR on this table that Bright Angel Bright 3-Mile House-South Rim 3 644 755 584 498 446 412 387 369 354 343 334 corresponds to your trail and estimated completion time. 1½-Mile House-South Rim 1.5 345 792 516 424 378 350 332 319 309

Colorado River-South Rim 7 1481 832 714 635 579 536 503 477 456 438 422 409 398 388

Colorado River-Little Panorama 0.75 232 611 426 364 333 314 302 293 1. body weight (lbs) + pack weight (lbs) = CF 154 lbs Colorado River-Panorama Point 1.5 372 835 538 438 389 359 339 325 314 306 2. CF x metabolic rate on table = your est. MR Colorado River-Skeleton Point 4 860 698 584 515 469 437 412 393 378 365 355

Colorado River-Cedar Ridge 5.5 1119 688 598 538 496 464 439 419 403 389 378 368

South Kaibab Skeleton Point-South Rim 3 622 738 572 489 439 406 382 365 351 340 331 3. If your estimated MR is greater than 500 kcal/hr, wait until cooler weather to hike. Or, Cedar Ridge-South Rim 1.5 347 795 518 425 379 351 333 319 309 take longer to complete the hike by slowing your pace, and increase the frequency and/or length of Ooh-Aah Point-South Rim 0.75 238 621 430 367 335 316 303 294 breaks.

Phantom Ranch-North Rim 14 1911 852 750 677 622 580 546 518 495 475 458 444 431 420 410

Phtm Ranch-mouth of Phantom Creek 2 82 371 306 284 273 266

Phantom Ranch-Cottonwood Camp 7.3 448 598 479 419 383 360 342 330 320 312 305 300 ** Approximate one-way distance (in miles) is from Phantom Ranch-Roaring Spring 9.5 814 674 566 501 457 426 403 385 370 358 349 340 333 North Kaibab Phantom Ranch Ranger Stn. For SK and BA trails, Cottonwood Camp-Supai Bridge 4 610 565 484 435 403 379 362 348 338 approximate elevation changes Phantom Ranch-Sumner Wash 2 381 850 545 443 392 362 342 327 316 308 (in meters) are from the lowest elevation in the canyon, the Phantom Ranch-Clear Creek Trail end 9.2 521 657 518 448 407 379 359 344 333 323 river bank. Misc. Phantom Ranch-Utah Flats 1 405 888 564 456 402 370 348 333 321 312

Page 24 Health Hazard Evaluation Report No. 99-0321-2873 Table 3: Physiological Measurement Results—collected while participants hiked from Phantom Ranch up to the South Rim Grand Canyon National Park, HETA 99-0321-2873

ty) " " ctivi f a o y ty) ty) rcent e tivi tivi excess" of 180 bpm c c n (p e i f a f a t e heart rate o o e CBT ling period g g ol/L) cent cent m otal activity minutes) cal/hour) vera eats per minute) er er vera os Ranger Date Samp (t Estimated(k metabolic rateHeartminus ra age A (b CBT(p in excess of 100.4°FCBT(p in excess of A101.3°F Change in bodyChange weight in sodiumChange (mEq/L) in BUNChange (mEq/L)(m in osmolalit A 6/26 16:15-20:36 661 19:43-20:34 122 18:48-20:36 19:45-20:36 100.2°F -1.9% 0.0 4.0 1.0 (262) (20%) (41%) (20%) )) B 6/27 05:34-12:30 457 07:32-07:54; Did not 100.0°F -0.8% -4.0 8.0 -6.9 (417) 08:16-08:41 exceed (13%) C1 6/27 11:16-15:05 713 11:48-13:35; 148 14:08-15:05 Did not 100.0°F) -1.7% -3.0 1.0 6.2 (230) 13:46-14:57 (25%)) exceed) (77%) D( 6/28 05:03-09:17 734 07:35-08:27; 136 06:44-07:08; 07:46-08:35 100.5°F -1.1% -1.0 3.0 -1.1 (255) 08:37-09:17 07:41-09:17 (19%) (37%) (47%) C2 6/30 08:46-13:58 611 09:29-10:02 134) 13:05-13:58 Did not 100.0°F -1.5% 0.0 3.0 1.0 (313) (11%)) (17%) exceed E( 7/04 04:03-08:36 605 04:40-04:50; 120 Did not Did not 98.8°F -1.1% -2.0 2.0 -1.8 (274) 05:26-05:45; exceed exceed 06:53-07:24 (23%) F1 7/04 02:36-07:20 585 05:45-06:17; 123 03:36-05:15; Did not 100.4°F -1.3% 1.0 11.0 3.5 (285) 06:26-07:12 05:42-07:20 exceed (28%) (70%) " These are the main criteria used to evaluate heat strain. CBT = core body temperature. ) Not all data available because of equipment failure or failure to wear equipment, which can over- or underestimate the participant’s results. ( Indicates this participant hiked the Bright Angel trail; all others hiked the South Kaibab trail.  Indicates maintenance and Park Service employees and others assisting with patrolling activities. Numbers in bold indicate the participant exceeded the recommended NIOSH or ACGIH limits.

Health Hazard Evaluation Report No. 99-0321-2873 Page 25 Table 4: Physiological Measurement Results—collected while participants hiked from the South Rim down to Phantom Ranch Grand Canyon National Park, HETA 99-0321-2873

ty) " " ctivi f a o y ty) ty) rcent e tivi tivi excess" of 180 bpm c c n (p e i f a f a t e heart rate o o e CBT ling period g g ol/L) cent cent m otal activity minutes) cal/hour) vera eats per minute) er er vera os Ranger Date Samp (t Estimated(k metabolic rate Heartminus ra age A (b CBT in(p excess of 100.4°FCBT in(p excess of 101.3°FA Change in bodyChange weight in sodiumChange (mEq/L) in ChangeBUN (mEq/L)(m in osmolalit

)) **** C3 6/27 18:30-21:16 313 19:24-21:16 Did not 100.2°F (167) (68%) exceed

)) F2 6/27 06:58-11:02 289 10:38-10:55 Did not 99.0°F) -1.3% 2.0 1.0 3.4 (245) (7.3%)) exceed)

))) G10 6/27 04:40-08:58 253 07:15-07:24; 116 -1.1% 7.0 7.0 16.4 (259) 08:31-08:58 (15%)

)) H 7/04 07:12-10:12 394 09:30-09:37; 09:56-09:59 99.9°F -1.2% 8.0 8.0 17.5 (181) 09:42-10:07 (2.2%) (16%)

I1 7/04 06:54-10:40 302 09:59-10:09; 126 10:07-10:13 Did not 99.5°F -1.2% -1.0 1.0 1.83 (227) 10:33-10:38 (2.6%) exceed (6.6%) " These are the main criteria used to determine heat strain. CBT = core body temperature. ) Not all data available because of equipment failure or failure to wear equipment, which can over- or underestimate the participant’s results. 0 Indicates a volunteer ranger.  Indicates maintenance and Park Service employees and others assisting with patrolling activities. * This parameter not measured. Numbers in bold indicate the participant exceeded the recommended NIOSH or ACGIH limits.

Page 26 Health Hazard Evaluation Report No. 99-0321-2873 Table 5: Physiological measurement results—collected while participants patrolled the South Rim and from 1-4.5 miles into the canyon Grand Canyon National Park, HETA 99-0321-2873

" " f o y cent ty) ty) er L excess of 180 bpm tivi tivi n " c c (p f a f a te i e heart rate o o e CBT ling period g g ol/L) cent cent m otal activity minutes) cal/hour) vera eats per minute) er er vera os PSAR Date Samp (t Estimated(k metabolic rate Heartminus ra activity) age A (b CBT(p in excess of 100.4°F CBT in(p excess of 101.3°F A Change in bodyChange weight in Changesodium (mEq/L)in ChangeBUN (mEq/L)(m in osmolalit J0 6/27 10:53-19:19 352 16:27-16:34; 17:28-17:53; 113 17:50-17:52 Did not 99.3°F) -1.7% -2.0 4.0 -0.4 (507) 18:24-18:40 (0.6%)) exceed) (10%) K0 6/28 07:46-15:54 281 10:37-10:53 105 10:40-11:09; 11:17-11:30; Did not 99.8°F -0.3% 2.0 0.0 4.4 (489) (3.5%) 15:24-15:54 exceed (15%) L0( 6/28 07:39-13:28 276 Did not exceed 85 10:57-11:21 Did not 99.4°F -1.1% 2.0 -1.0 4.0 (350) (7.1%) exceed M0 6/28 10:24-19:35 352 10:26-10:46; 10:55-11:21; 145) 12:07-12:17; 12:45-13:48; 13:01-13:47; 100.3°F) -1.2% -7.0 6.0 13.0 (552) 11:40-12:12; 12:41-13:59; 14:07-14:44; 16:34-17:22; (8.5%)) 16:18-16:32; 17:34-17:45; 18:27-19:31 18:20-18:39; 19:17-19:35 (42%)) (41%)) N 6/29 11:12-16:48 438 14:00-14:24 97 16:26-16:31 Did not 99.0°F) -0.8% -3.0 -2.0 -6.9 (337) (7.4%) (1.8%)) exceed) O0 6/29 11:00-20:14 334 11:41-11:46; 12:12-13:55; 159) 19:21-20:04 Did not 99.3°F) -0.6% 1.0 9.0 4.3 (555) 15:01-15:11; 15:29-15:41; (8.6%)) exceed) 15:57-16:09; 18:06-20:00 (47%)) " These are the main criteria used to evaluate heat strain. CBT = core body temperature. L These results were calculated by assuming the participant spent 2/3 of the activity ascending and 1/3 of the activity descending or walking on the flat. 0 Indicates a volunteer ranger. ) Not all data available because of equipment failure or failure to wear equipment, which can over- or underestimate the participant’s results. ( This PSAR patrolled the South Kaibab trail; all others patrolled the Bright Angel trail.  Indicates maintenance and Park Service employees and others assisting with patrolling activities. Numbers in bold indicate the participant exceeded the recommended NIOSH or ACGIH limits.

Health Hazard Evaluation Report No. 99-0321-2873 Page 27 Table 6: Physiological Measurement Results—collected while participants conducted inner-canyon patrol Grand Canyon National Park, HETA 99-0321-2873

" " f o y cent ty) ty) er L excess of 180 bpm tivi tivi ail n " c c (p f a f a tr te i d e heart rate o o e CBT ling period g g ol/L) olle cent cent m otal activity minutes) cal/hour) vera eats per minute) er er vera os Ranger Date Samp (t Patr Estimated(k metabolicHeart rate raminusactivity) age A (b CBT(p in excess of 100.4°F CBT in(p excess of 101.3°FA Change in bodyChange weight in Changesodium (mEq/L)in ChangeBUN (mEq/L)(m in osmolalit

) G20 6/28 09:36-13:50 Clear 304 151) Did not exceed Did not 98.7°F -2.3% 5.0 5.0 14.1 (255) Creek exceed

F3 7/02 11:30-14:20 Utah 426 11:43-11:51; 119 11:48-11:51 Did not 99.0°F) 0% 0.0 5.0 0.7 (171) Flats 12:00-12:02; (2.3%)) exceed) 12:13-12:35 (20%)

)) **** I2 7/04 13:42-17:56 B.A. to 297 14:25-15:12; 16:29-16:32; 14:49- 100.3°F (255) Pipeline 16:39-16:46; 16:54-17:25 14:52 Creek (36%) (1.6%) " These are the main criteria used to determine heat strain. CBT = core body temperature. L These results were calculated by assuming the participant spent 2/3 of the activity ascending and 1/3 of the activity descending or walking on the flat. 0 Indicates a volunteer ranger. ) Not all data available because of equipment failure or failure to wear equipment, which can over- or underestimate the participant’s results. * This parameter was not measured. B.A. is Bright Angel trail. Numbers in bold indicate the participant exceeded the recommended NIOSH or ACGIH limits.

Page 28 Health Hazard Evaluation Report No. 99-0321-2873 Table 7: Median Blood Analyte Results by Job Title Grand Canyon National Park, HETA 99-0321-2873

Job Title Analyte (normal values) Baseline Post Activity Change (Range)É

Sodium (135-145 mEq/L) 140 mEq/L 140 mEq/L 0 (-4 to 3) mEq/L Park Blood Urea Nitrogen (12-20 mg/dl) 14 mg/dl 18 mg/dl 4 (9 to 22) mg/dl Rangers Osmolality (275-290 mosmol/L) 290.4 mosmol/L 290.7 mosmol/L 1.1 (-6.9 to 6.2) mosmol/L

Sodium (135-145 mEq/L) 140 mEq/L 142 mEq/L 1.5 (-7.0 to 7.0) mEq/L

Volunteers Blood Urea Nitrogen (12-20 mg/dl) 11 mg/dl 16 mg/dl 4.5 (-1 to 9) mg/dl

Osmolality (275-290 mosmol/L) 286.9 mosmol/L 291.3 mosmol/L 4.2 (-13.0 to 16.7) mosmol/L

Sodium (135-145 mEq/L) 141 mEq/L 143 mEq/L 0 (-3 to 8) mEq/L Other Blood Urea Nitrogen (12-20 mg/dl) 20 mg/dl 22 mg/dl 2 (-2 to 12) mg/dl Employees Osmolality (275-290 mosmol/L) 293.2 mosmol/L 298.2 mosmol/L 1.2 (-6.8 to 18.8) mosmol/L É Each group’s change in analyte levels is noted here, with the ranges of all the individual analyte changes in parentheses.

Table 8: Median Blood Analyte Results by Activity Performed Grand Canyon National Park, HETA 99-0321-2873

Activity Analyte (normal values) Baseline Post Activity Change (Range)É

Sodium (135-145 mEq/L) 138 mEq/L 142 mEq/L 4.5 (-1 to 8) mEq/L Hike into Blood Urea Nitrogen (12-20 mg/dl) 13 mg/dl 17 mg/dl 4.0 (1 to 8) mg/dl Canyon Osmolality (275-290 mosmol/L) 285.7 mosmol/L 295.5 mosmol/L 10.1 (-6 to 17.5) mosmol/L

Sodium (135-145 mEq/L) 142 mEq/L 142 mEq/L 0 (-4 to 7) mEq/L Hike out of Blood Urea Nitrogen (12-20 mg/dl) 15 mg/dl 21 mg/dl 4(2 to 12) mg/dl Canyon Osmolality (275-290 mosmol/L) 293.9 mosmol/L 296.5 mosmol/L 1.1 (6.9 to 18.8) mosmol/L

Sodium (135-145 mEq/L) 140 mEq/L 140 mEq/L 0 (-7 to 5) mEq/L

Patrol Blood Urea Nitrogen (12-20 mg/dl) 14 mg/dl 16 mg/dl 2 (-2 to 9) mg/dl

Osmolality (275-290 mosmol/L) 289.2 mosmol/L 290.0 mosmol/L 0.1 (-13.0 to 14.1) mosmol/L É Each group’s change in analyte levels is noted here, with the ranges of all the individual analyte changes in parentheses.

Health Hazard Evaluation Report No. 99-0321-2873 Page 29 *Figure 1: Percent Decrease in Body Weight by Job Title Grand Canyon National Park, HETA 99-0321-2873

*Figure 2: Change in Serum Sodium Concentration by Job Title Grand Canyon National Park, HETA 99-0321-2873

*The boxplot shows the median (the horizontal line within the shaded area), interquartile range (shaded area), and extreme values for each group.

Page 30 Health Hazard Evaluation Report No. 99-0321-2873 *Figure 3: Percent Decrease in Body Weight by Activity Performed Grand Canyon National Park, HETA 99-0321-2873

*Figure 4: Change in Serum Sodium Concentration By Activity Performed Grand Canyon National Park, HETA 99-0321-2873

*The boxplot shows the median (the horizontal line within the shaded area), interquartile range (shaded area), and extreme values for each group.

Health Hazard Evaluation Report No. 99-0321-2873 Page 31 Figure 5: Acclimatization schedulesc Grand Canyon National Park, HETA 99-0321-2873

Work Schedule for Heat Acclimatized and Unacclimatized Employees (Based on a 10-hour shift)

10 100% 100% 9 8 80% 80% 7 6 60% 60% Unacclimatized 5 50% 40% Acclimatized 4 Shift Hours Shift 3 2 20% 1 0 Day One Day Two Day Three Day Four Day Five Day of Work Week

c This illustration was created for this report from information in NIOSH [1986]. Criteria for a recommended standard: occupational exposure to hot environments, rev. Cincinnati, OH: U.S. Dept. of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 86-113.

Page 32 Health Hazard Evaluation Report No. 99-0321-2873 Appendix A: Assessment of Work Estimated Metabolic Heat Production Rates by Task Analysis10

A. Body Position and Movement kcal/min* Sitting 0.3 Standing 0.6 Walking (uphill) 2.0 - 3.0 (add 0.8 kcal/meter rise in elevation)

B. Type of Work Average (kcal/min) Range (kcal/min) Hand work: light 0.4 0.2 - 1.2 heavy 0.9 Work, one arm: light 1.0 0.7 - 2.5 heavy 1.8 Work, both arms: light 1.5 1.0 - 3.5 heavy 2.5 Work, whole body: light 3.5 2.5 - 9.0 moderate 5.0 heavy 7.0 very heavy 9.0

C. Basal Metabolism 1.0 1.0 Sum of A, B, and C equals estimated metabolic production per task *For a standard male worker of 70 kg (154 lbs) body weight and 1.8 m2 (19.4 ft2) body surface. ______

1. Sample calculation for hiking out of the Grand Canyon on SK trail (ranger A):

Task kcal/min A. Walking - 3.0 kcal/min - walking uphill, add 0.8 kcal per meter risen - 4.5 kcal/min† B. ‘Type of Work’ - 0 kcal/min C. Basal metabolism - 1.0 kcal/min Metabolic Rate Total - 8.5 kcal/min x 60 min/hour = 510 kcal/hour

D. Multiply by the weight correction factor - 510 kcal/hour x 1.29‡

Total estimated metabolic rate = 661 kcal/hour

† Ranger A hiked out in 262 minutes. The change in elevation from Phantom Ranch to the South Rim via the South Kaibab trail is 1,481 meters. Therefore, ranger A’s estimated average metabolic rate only for hiking uphill was 1,481 meters ÷ 262 minutes = 5.7 meters/min x 0.8 kcal/meter = 4.5 kcal/min.

‡ The weight correction factor is used when an employee plus his/her pack or load weigh other than 154 lbs. The factor is calculated by dividing the sum of the employee’s current body weight (BW) and the pack weight (PW) by 154 lbs or ([BW + PW] ÷ 154 lbs = weight correction factor). Ranger A’s correction factor on the day of the study was calculated as: (159 lbs + 40 lbs) ÷ 154 lbs = 1.29.

Health Hazard Evaluation Report No. 99-0321-2873 Page 33 Appendix A: Assessment of Work (continued) Estimated Metabolic Heat Production Rates by Task Analysis10

2. Sample calculation for hiking into the Grand Canyon on SK trail (ranger C3):

Task kcal/min A. Walking - 3.0 kcal/min - walking downhill - 0 kcal/min† B. ‘Type of Work’ - 0 kcal/min C. Basal metabolism - 1.0 kcal/min Metabolic Rate Total - 4.0 kcal/min x 60 min/hour = 240 kcal/hour

D. Multiply by the weight correction factor - 240 kcal/hour x 1.31‡

Total estimated metabolic rate = 313 kcal/hour

† Ranger C3's descent took 167 minutes. No metabolic cost is added for hiking downhill.

‡ The weight correction factor is used when an employee plus his/her pack or load weigh other than 154 lbs. The factor is calculated by using the equation: (BW + PW) ÷ 154 lbs = weight correction factor. Ranger C3’s correction factor on the day of the study was calculated as: (161 lbs + 40 lbs) ÷ 154 lbs = 1.31. ______

3. Sample calculation for hiking out of the Grand Canyon on SK trail in 4 hours versus 5½ hours:† Task 4 hours 5½ hours A. Walking - 3.0 kcal/min 3.0 kcal/min - walking uphill, add 0.8 kcal per meter risen 4.9 kcal/min 3.6 kcal/min B. ‘Type of Work’ - 0 kcal/min 0 kcal/min C. Basal metabolism - 1.0 kcal/min 1.0 kcal/min Metabolic rate total 8.9 kcal/min x 60 min/hour 7.6 kcal/min x 60 min/hr

Total estimated metabolic rate = 536 kcal/hour* versus 456 kcal/hour*

† Lengthening the average time of ascent by 90 minutes reduces the estimated metabolic rate by 80 kcal/hr and brings the rate within the NIOSH REL/RAL levels of 100-500 kcal/hr.

* These rates do not include a weight correction factor.

Page 34 Health Hazard Evaluation Report No. 99-0321-2873 10, d Appendix B: NIOSH Recommended Heat-Stress Alert and Heat-Stress Exposure Limits

A A

d The figures’ curves indicate recommended work/rest regimens for a combination of external heat (measured as wet-bulb globe temperatures) and internal (metabolic) heat. The ‘C’ curve is the Ceiling Limit, indicating that workers should not be exposed to such conditions without adequate heat-protective clothing and equipment.10

Health Hazard Evaluation Report No. 99-0321-2873 Page 35 Figure 1. Recommended Heat-Stress Alert Limits (Unacclimatized Workers) Figure 2. Recommended Heat-Stress Exposure Limits (Acclimatized Workers)

Page 36 Health Hazard Evaluation Report No. 99-0321-2873 Appendix C: ACGIH Evaluation Scheme for Heat Stress*

Heat Stress Expected

NO Does clothing allow air or water vapor movement? (See Section 1) YES

NO Are screening criteria in Table 2 exceeded? Low risk (See Section 2) YES Continue work, NO monitor conditions Are data available for detailed analysis? (See Section 3) Continue work, maintain controls, YES monitor conditions NO Excessive heat stress based on detailed analysis? Implement general controls (See Section 3) (See Section 5) YES

Perform heat-strain (physiological) monitoring (See Section 4)

NO Excessive heat strain based on detailed analysis? (See Section 4) YES

Implement job-specific controls (See Section 5) * From American Conference of Governmental Industrial Hygienists (ACGIH®), 2001 TLV® and BEI® Documentation and 2000 Supplement: Heat stress and strain: Documentation of TLVs® and BEIs®, 6th Edition. Copyright 2000 and 2001, respectively. Reprinted with permission

Health Hazard Evaluation Report No. 99-0321-2873 Page 37 Appendix D: ACGIH Screening Criteria for Heat Stress Exposure*

Acclimatized (WBGT values in °F) Unacclimatized (WBGT values in °F) Work Light Moderate Heavy Very Light Moderate Heavy Very Demands Heavy Heavy 100% Work 85.1 81.5 78.8 81.5 77.0 72.5 75% Work; 86.9 83.3 81.5 84.2 79.7 76.1 25% Rest 50% Work; 88.7 85.1 83.3 81.5 86.0 82.4 79.7 77.0 50% Rest 25% Work; 90.5 87.8 86.0 85.1 87.8 84.2 82.4 79.7 75% Rest Notes: < See work demand categories table below. < WBGT values represent thresholds near the upper limit of the metabolic rate category. < If work and rest environments are different, hourly time-weighted averages (TWA) should be calculated and used. TWAs for work rates should also be used when the work demands vary within the hour. < Values in the table assume 8-hour workdays in a 5-day workweek with conventional breaks as discussed in the Evaluation Criteria section of this report. < Because of the physiological strain associated with Very Heavy work among less fit workers regardless of WBGT, criteria values are not provided for continuous work and for up to 25% rest in an hour. The screening criteria are not recommended, and a detailed analysis and/or physiological monitoring should be used.

The following work load categories, descriptions of work, and estimated energy expenditures help to estimate a conservative WBGT heat exposure limit for workers conducting these or similar jobs:

Work Categories Example Activities Resting Sitting quietly; Sitting with moderate arm movements Light Sitting with moderate arm and leg movements; Standing with light (<200 kcal/hr) work at machine or bench while using mostly arms Scrubbing in a standing position; Walking about with moderate lifting Moderate or pushing; Walking on level at 3.7 mph while carrying a 6.6 pound (200-350 kcal/hr) load Carpenter sawing by hand; Shoveling dry sand; Heavy assembly work Heavy on a noncontinuous basis; Intermittent heavy lifting with pushing or (350-500 kcal/hr) pulling (e.g. pick-and-shovel work) Very Heavy Shoveling wet sand (>500 kcal/hr)

* From American Conference of Governmental Industrial Hygienists (ACGIH®), 2001 TLV® and BEI® Documentation and 2000 Supplement: Heat stress and strain: Documentation of TLVs® and BEIs®, 6th Edition. Copyright 2000 and 2001, respectively. Reprinted with permission.

Page 38 Health Hazard Evaluation Report No. 99-0321-2873 Appendix E: Use of Personal Monitoring Methods to Reduce Heat-Related Illnesses10

Periodic monitoring of the heart rate, oral temperature, extent of body weight loss, and/or recovery heart rate should always include the determination of baseline values for deciding whether individuals are fit to continue work that day.

UHeart rate: Calculate your heart rate limit by subtracting your age from 180. Your heart rate at peak work effort should not exceed this number for more than 3 or 4 minutes. If it does, stop work immediately, find some shade, drink, and rest until your heart rate returns to a more normal pace. Repeat as necessary.

U Oral Temperature:10 Use a clinical thermometer right after stopping work but before drinking anything. Try to avoid open-mouth breathing prior to inserting the thermometer, as well. If the oral temperature taken under the tongue exceeds 99.7°F, shorten the next work cycle by one-third and maintain the same rest period. An oral temperature of 100.4°F (deep body temperature of 102.2°F) should be considered reason to terminate exposure even when temperature is being monitored.

U Body Weight: Monitor hydration status on a regular basis. Thirst is a poor indicator of hydration because significant dehydration has already taken place when the thirst sensation occurs. Workers should be familiar with their weight when they are fully hydrated and should strive to maintain this weight. Weight loss should not exceed 1.5% of total body weight in a work day. If it does, fluid and food intake should increase. (Alcohol and caffeinated beverages should always be avoided when working under heat stress conditions.) Workers should attempt to re-hydrate themselves until they achieve their baseline weight. For this purpose, accurate scales should be made available at every work station. Body water loss can be measured by weighing the worker at the beginning and end of each work day and by using this equation:

(pre-activity weight - post-activity weight) ÷ pre-activity weight × 100 = % body weight lost

U Recovery Heart Rate:10 Following a normal work cycle, compare a pulse rate taken at 3 minutes of

seated rest, P3, with the pulse rate taken at 1 minute of rest, P1. Interpret the results using the following table:

Heart Rate Recovery Pattern P3 P1 minus P3 Excessive heat strain: š90 bpm and ˜10 bpm

Moderate strain: š90 bpm and š10 bpm

Sufficient recovery: —90 bpm and ™10 bpm

Health Hazard Evaluation Report No. 99-0321-2873 Page 39 DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Institute for Occupational Safety and Health 4676 Columbia Parkway Cincinnati, OH 45226-1998

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